i

MONOGRAPHS IN AEROSPACE HISTORY #16

by

Tom Tucker

Touchdown:

The Development

of Propulsion

Controlled

Aircraft at

NASA Dryden
ii

Touchdown: The Development of

Propulsion Controlled Aircraft

at NASA Dryden

by

Tom Tucker

NASA History Office

Office of Policy and Plans

NASA Headquarters

Washington, DC 20546

Monographs in

Aerospace History

Number 16

1999
iii
iv

Table of Contents

Foreword............................................................................................................. iv

Preface ................................................................................................................. v

The Development of Propulsion Controlled Aircraft at NASA Dryden.............. 1

Appendices

Appendix A: Aircraft Accident Report, United Airlines Flight 232 ............ 36

Appendix B: Flight Simulator Studies ........................................................ 38

Appendix C: National Transportation Safety Board Recommendation ...... 39

Appendix D: Guest Pilot Comments on . . . F-15........................................ 40

Appendix E: PCA System Landing in MD-11 Aircraft ............................... 46

Appendix F: Summary of Guest Pilot Comments about . . . MD-11 .......... 47

Appendix G: Awards and Honors [for the PCA Team] ............................... 50

Index .................................................................................................................. 51

About the Author ............................................................................................... 54
v

Foreword

This monograph relates the important history of the Propulsion Controlled

Aircraft project at NASA’s Dryden Flight Research Center. Spurred by a

number of airplane crashes caused by the loss of hydraulic flight controls, a

NASA-industry team lead by Frank W. Burcham and C. Gordon Fullerton

developed a way to land an aircraft safely using only engine thrust to control the

airplane.

In spite of initial skepticism, the team discovered that, by manually manipulating an airplane’s thrust, there was adequate control for extended up-and-away

flight. However, there was not adequate control precision for safe runway

landings because of the small control forces, slow response, and difficulty in

damping the airplane phugoid and Dutch roll oscillations. The team therefore

conceived, developed, and tested the first computerized Propulsion Controlled

Aircraft (PCA) system. The PCA system takes pilot commands, uses feedback

from airplane measurements, and computes commands for the thrust of each

engine, yielding much more precise control. Pitch rate and velocity feedback

damp the phugoid oscillation, while yaw rate feedback damps the Dutch roll

motion.

The team tested the PCA system in simulators and conducted flight research in

F-15 and MD-11 airplanes. Later, they developed less sophisticated variants of

PCA called PCA Lite and PCA Ultralite to make the system cheaper and therefore more attractive to industry. This monograph tells the PCA story in a nontechnical way with emphasis on the human aspects of the engineering and

flight-research effort. It thereby supplements the extensive technical literature

on PCA and makes the development of this technology accessible to a wide

audience. I commend this brief account to anyone interested in the progress of

aviation technology.

Kevin L. Petersen

Director, Dryden Flight Research Center

18 February 1999
vi

Preface

Many histories of invention look back over decades and even centuries to tell their

tale. But another perspective comes from the middle of the process, when the

outcome is uncertain, when questions remain, when the invention and development

process remain a “hazard of fortune.” It is a rewarding experience to view developing technology from this angle. The story of the invention and development of

Propulsion Controlled Aircraft at NASA Dryden Flight Research Center made this

point again and again to me in the summer of 1998 as I researched the invention

within several hundred yards of where only several years before, the first jumbo jet

lumbered in for a safe landing using the new technology.

I owe a great debt to the many individuals, programs, and organizations which

enabled me to write this history. First, I am grateful to the NASA - ASEE Summer

Faculty Fellowship Program which brought me to NASA Dryden Flight Research

Center out in the Mojave Desert and supplied me with every kind of support needed

for research and writing. At Dryden Center, Don Black and Kristie Carlson provided

much courtesy and good advice. At the Stanford University Department of Aeronautics and Astronautics, Melinda Francis Gratteau, Program Administrator, and

Michael Tauber, Co-director of the Program, aided me invaluably with their help,

consideration, and provision of opportunities. The participatory programs they

offered to me and other NASA ASEE fellows at the NASA Ames Research Center

helped me in thinking about and clarifying this invention history project.

Many people inside and outside NASA gave generously of their time and expertise

in interviews and correspondence. These included: Russ Barber, Bob Baron, John

Bull, Bill Burcham, John Burken, Joe Conley, Bill Dana, Dwain Deets, Michael

Dornheim, John Feather, Dennis Fitch, Gordon Fullerton, Glenn Gilyard, Al

Haynes, Tom Imrich, Jeff Kahler, Yvonne Kellogg, John Lauber, Jeannette Le,

Trindel Maine, John Miller, Terry Neighbor, Drew Pappas, Dana Purifoy, Joel Sitz,

Walt Smith, Jim Smolka, Jim Stewart, Ken Szalai, Jim Urness, Tom Wolf, and Bob

Yeager.

Readers of drafts along the way offered many valuable comments. I especially

thank: Bill Burcham, Roger Launius, Trindel Maine, and John Miller. I am grateful

to Dennis Ragsdale of the NASA Dryden Library for tracking down my numerous

research requests. Steven Lighthill and the NASA Dryden Graphics Department as

well as the NASA Dryden Photo Lab went above and beyond the call of duty in

giving this project the benefit of their talents. Camilla McArthur deserves recognition for her expert work arranging for the printing of the monograph through the

Government Printing Office.

Last and most, I owe a debt to Dill Hunley, chief editor, advisor, facilitator, and

friend who throughout the process made this history much better than it could have

been through my efforts alone.

Tom Tucker

Spindale, NC

12 April 1999
vii

Touchdown:

The

Development

of Propulsion

Controlled

Aircraft at

NASA

Dryden

At 30,000 feet altitude flying to St. Louis

on a business trip, Bill Burcham, then

Chief Propulsion Engineer at NASA’s

Dryden Flight Research Center, had an

idea that would change his life. It was a

late summer day in 1989. Burcham

pushed aside his well-thumbed copy of

the trade journal Aviation Week & Space

Technology. As the peaceful routine of the

commercial flight went on, he began to

draw. He began a sketch on the back of a

TWA cocktail napkin.

Burcham, a thirty-three year veteran in

aeronautics at NASA, is well-known to

his colleagues as a man whose emotions

even in emergency never modulate

beyond matter-of-fact. So there were no

Eureka shouts. There was only his pen

dancing over paper.

 The spark that started him thinking was

the latest in a series of articles appearing

that summer about a major jet crash.1 On

19 July 1989, a widebody jet had experienced disaster during a routine flight over

Iowa farmlands. The rear engine had

blown out. The loss of this engine’s thrust

was not central to the mayhem that

followed. In fact, the two other engines

slung under the wings remained sufficient

for somewhat regular flight. But the

hydraulic system had vanished. The

hydraulics operate all the controls that a

pilot uses to control flight. The airplane

had three hydraulic systems, any two of

them capable of providing almost normal

control, and any one capable of providing

a safe landing, but the shrapnel from the

explosion had taken out all three. Suddenly, the control wheel was dead in the

pilot’s hand.

Figure 1. Bill

Burcham’s PCA

napkin, showing

the diagram of

Dryden’s Propulsion Controlled

Aircraft project. In

the diagram,

DEFCS stands for

Digital Electronic

Flight Control

System, a computerized system that

provides digital

flight controls;

HIDEC stands for

Highly Integrated

Digital Electronic

Control. (NASA

photo EC94-42805-

1 by Dennis

Taylor).

1 See Frank W. Burcham, “Cleared for Landing,” Air & Space (April/May 1995): 20-21.

1
viii

As the plane moved bizarrely across the

sky and the flight attendants wheeled

back meal carts unserved and passengers

stirred uneasily, the crew wrestled with

the problem of landing the airplane.

Captain Al Haynes and Dennis Fitch, an

airline check pilot who had hurried

forward to help in the cockpit, made a

discovery. By nudging the throttles to the

two remaining engines, they could herd

the airplane across the skies. Flight

controllers contacted the crew and

directed the airplane to the Sioux Gateway Airport at Sioux City, where emergency preparations had already begun. At

1600 hours, the airliner made a crash

landing on Runway 22. It cartwheeled

during touchdown, yet 184 of the 296 on

board survived the crash and ensuing

fire.2

“Could I come up with something that

would have helped those fellows?”

Burcham remembers thinking. He continued to sketch on the napkin. On the fourinch-square plane of soft tissue appeared

an idea big enough perhaps to prevent

similar disasters in the future.

What he scratched down was a schematic

diagram.3 He showed his drawing to

project manager Jim Stewart, the friend

and NASA associate seated next to him.

They bounced concepts back and forth.

“He thought it was a great idea,” remembers Burcham, “and within five minutes

we had outlined a test program.”4

His idea was a backup landing technique

for an airplane that has lost all normal

flight controls. Burcham wondered if he

could maneuver a crippled airplane to a

safe landing by harnessing the brute force

of the engines. He would exploit some

technology available in recent airplanes.

These new aircraft had digital flight

control computers. They also had digital

engine control computers that ran the

engines. Why not program these digital

computers to provide enough control for a

touchdown? At that time, educated opinion

Figure 2. The F-15

flown in the HIDEC

program and also

PCA. (NASA photo

EC86-33538-2

Fr23 by Mike

Smith).

2 See David Hughes and Michael Dornheim, “United DC-10 Crashes in Sioux City, Iowa,”

Aviation Week & Space Technology (24 July 1989): 96-97; National Transportation Safety Board

Aircraft Accident Report, United Airlines Flight 232, McDonnell Douglas DC-10-10, Sioux

Gateway Airport, Sioux City, Iowa, July 19,1989 (Washington, DC, 1989). Appendix A of this

monograph reproduces details from the latter source.

3 Frank W. Burcham, interview with author, 15 June 1998, as well as 6 other interviews with

author over summer of 1998.

4 Burcham interview, 15 June 1998.

2
ix

would have been that if you tried to land

an airplane on a runway with this technology, you would end up with a smoking

hole in the ground.

* * *

Out in the Mojave Desert 70 miles

northeast of Los Angeles are the plain

offices, metal shacks, and hangars that

comprise the NASA Dryden Flight

Research Center on Edwards Air Force

Base. The ancient dry lakebed gleams in

the afternoon sun as if it were a fantastic

illustration for a science fiction paperback. But even more paradoxical are the

labs and offices where on battered federal

desks dating back two generations,

concepts for use in the aircraft of the next

millennium are born and developed.

Despite NASA’s charter commitment to

commercial air safety innovation, it was

also, by many standards, a strange site for

Burcham’s idea.5

The napkin scheme did not initially come

to life with the dignity of a project with a

budget, but for months Burcham pushed it

along in an hour snatched at the end of a

week. Or after a day’s flight, he would

call the research pilot and in his affable,

low-key manner inquire, “Gotta hundred

pounds of extra gas; could you try this

backup card test point?” The researchers

have names for this type of investigation—they call it “bootlegging” or

“piggybacking” or “in the noise” (an

engineer’s term for experimental efforts

so minimal they can be neglected). No

dramatic leaps greeted this effort, which

was to become for Burcham something

near a quest. The path was evolution

rather than revolution.

Stewart and Burcham had been exploring

a new technology known as HIDEC,

Highly Integrated Digital Electronic

Control, an attempt to optimize engine

performance to match the flight conditions of the aircraft by integrating engine

and flight control systems. A follow-on

activity involved doing on-board diagnostics when an airplane was damaged and

then reconfiguring what remained functional to fly the airplane.6

5 Although NASA’s Dryden Flight Research Center and its predecessor organizations have an illustrious history of flight

research on a wide variety of aircraft, other NASA centers have traditionally been more closely associated with transport

technology.

6 Despite the temptation to trace connections between HIDEC and Burcham’s new project for landing aircraft with

engine control—which came to be called Propulsion Controlled Aircraft (see below in narrative)—and to view the earlier

project as a conceptual starting point for the later one, these are quite distinct programs. In editorial notes to this text,

Dryden engineer Trindel Maine cautioned, “HIDEC really wasn’t primarily a reconfiguration program, though at least

one reconfiguration program was flown under its auspices. Primarily it was a series of experiments designed to discover

and demonstrate the benefits of going to computer-controlled engines. This included a greater ability to recognize engine

problems, change engine setting depending on the situation, and cut out excess operating margins.”

3
x

Figure 4. Diagram of a Dutch roll.

“We had already looked at engines,”

recalls Stewart; “that is one thing all these

planes have in common.”7 It was a glance

merely, a preliminary study, no proof. But

the engineers had already looked into

reconfiguration enough to speculate that if

more than one control surface did not

function, the airplane was in trouble. To

lose them all and depend on engine thrust

alone would be, in effect, the ultimate

reconfiguration. In the pantheon of badcase scenarios, this was the worst.

Passengers on a commercial flight may

instinctively sense that destiny is in the

control of the big engines, the big airframe.

But the most crucial parts are the narrow

metal strips: the ailerons on the back of

the wings, the rudder, and the elevators

on the back of the tail fins that control

flightpath. These strips also dominate

certain unbalanced motions no pilot

wants unleashed, motions known as the

phugoid oscillation and the Dutch roll

oscillation.

You experience phugoid oscillations in

almost any air flight. They probably

make an appearance as no more than

slight nibbles in a smooth passage,

arising so gradually that normally the

pilot touches the wheel and kills the

oscillation without thinking about it.

The phugoid is a pitching motion in

which kinetic and potential energy (speed

and altitude) are traded. Each cycle of the

oscillation typically lasts about 60

seconds and may continue for many

minutes. As the airplane’s nose pitches

to the highest point, speed slows. As the

nose drops back toward the middle of the

cycle, speed increases. The experience

resembles a sort of eerie slow-motion

roller coaster ride. Its effect on landings

can be fatal if the motion continues

uncontrolled near the ground.

The second oscillation is known as the

Dutch roll (named for the motion of an ice

skater). According to one NASA research

pilot, an airplane in the Dutch roll mode

“resembles a snake slithering.”8 Obviously, this is not a desirable way to travel

off the ground. This complex oscillation

combines several factors including yaw,

roll, dihedral effect, lift, and drag. In a

7 James Stewart, interview with author, 10 June 1998.

8 Dana Purifoy, interview with author, 2 July 1998.

4
xi

Figure 5. An early

acronym and also

a sample of Bill

Burcham’s

viewgraph

expertise

Dutch roll, the airplane’s nose typically

rotates through about three degrees.

When an airplane tries to find the runway,

there is only about one degree of margin

for safe runway touchdowns.9

Although concern with these mysterious

oscillations lay on the horizon before

Burcham’s technology, the project had a

clear, specific goal—to land a jumbo jet

using engine thrust alone. None of the inbetween steps were well defined and

some would not, as it turned out, resolve

themselves for years. Any proposed

change to passenger aircraft requires

endless refining tests, proof upon proof to

check the vast web of real flight possibility. The Federal Aviation Administration

(FAA), the National Transportation Safety

Board (NTSB), the manufacturer, the

airlines, and various associations and

advisory groups are all part of the mesh.

But the unknowns stretched beyond

regular procedures. “We had to ask basic

questions,” recalls Jim Stewart. “Can you

control the airplane [this way]? And some

here were saying no.”10

Burcham had already devised an acronym

for the project. The typical NASA project

generates several acronyms in its lifetime.

To outsiders, the engineers who coin these

names may seem like techies taking their

revenge on the English language. The

acronyms are born and die—few of them

ever survive as standard usage, and they

sometimes change on the same project

from report to report. You need a

scorecard to read these reports, continually referring to the inevitable “Nomenclature” section appearing on page one

right beneath the “Abstract.” Along the

9 See Donna Gerren, “Design, Analysis, and Control of Large Transport Aircraft utilizing Engine Thrust as a Backup

System for the Primary Flight Controls” (unpublished thesis, University of Kansas, Feb. 1993): 20-22. This thesis was

later published as NASA CR-186035 in October of 1995.

10 Stewart interview.

5
xii

Figure 6. The

Dryden F-15

simulator cockpit.

way the project was known as PROTECT

(PROpulsive Techniques for Emergency

ConTrol), POC (Propulsion Only Control), and PROFAC, an acronym that

today causes all concerned to scratch their

heads when asked to explain its forgotten

origin. Marketing may be the true mainspring behind these verbalizations. A good

acronym resonates. “If you don’t have a

good acronym,” offers one engineer,

“you’re dead in the water.”11 The ultimate

acronym, coined by industry, turned out to

be PCA, Propulsion Controlled Aircraft.

The first step for PCA was to see if a pilot

could alter the course of the airplane

simply by working the throttles. To test

this, Burcham went to veteran simulations

engineer Tom Wolf. “Can you lock down

all the flight controls on a sim [simulation]?” he asked.

The next morning, Wolf had the sim

ready. He had altered the F-15 sim, a

model of a high performance fighter

airplane that he and Burcham used as a

testbed for HIDEC projects. Burcham, a

skilled amateur pilot, climbed in the

cockpit. First, he tried the lateral movement. Could he turn the F-15? “I found

that by advancing one throttle and retarding the other,” recalls Burcham, “the F-15

rolled nicely, even though the engines are

close together.”

Next, he pushed both throttles up a bit.

When he did, the airplane nosed up

slightly. If he cut both throttles back, the

nose dipped. He had demonstrated some

longitudinal control. In the excitement, all

in a lunch hour away from his primary

project, he moved on to the next step, the

simulated landing itself. Unfortunately,

his exhilarating video screen journey

came to an end when he crashed short of

the imaginary runway.

Burcham continued step-by-step. He was

doing what Denny Fitch had done on

Flight 232. He called it Throttles Only

11 John Burken, interview with author, 9 June 1998.

6
xiii

Control (TOC).12 It was a necessary step,

not a destination. But with repeated

practice, he managed to use TOC to land

the F-15 in the simulation. “There seemed

to be enough brute force there,” he said,

“that I felt with a computer providing

some finesse, safe landings would be

possible.”13

* * *

Glenn Gilyard is a 55-year-old senior

Dryden controls engineer who specializes

in computer-assisted controls. A large man

whose eyes gleam with elfin humor, he

recalls his first encounter with PCA.

Kevin Petersen, Chief of the Vehicle

Technology Branch in the Research

Engineering Division, approached him

one afternoon in 1990. Despite the

skepticism at the Center, Petersen was

intrigued by PCA and hesitantly asked

Gilyard if he would put some time into

the project.

“I jumped on it right off the bat,” says

Gilyard, “This appeared feasible.”

Gilyard looked at the solution as an

autopilot function. He had worked on

innovative solutions for the auto-throttle

of the YF-12. What if he used the pilot’s

control stick to command direction? The

input would go through the flight computer, which would also receive sensor

feedback from the airplane and use it to

calculate and move the throttles.

Where would they get the sim airplane to

make the control tests? Although the F-15

simulation had already been used, in the

corner of the lab rested another sim from

an abandoned project—a four-engine

transport, the Boeing 720. There was not a

real Boeing 720 waiting outside on the

Edwards base runway to take investigation to the next level. Rather, it was the

only transport simulation available.

Gilyard’s eyes gleam with mischief when

he explains why the sim but no airplane

was available. Once Dryden did employ a

real Boeing 720 for use in experiments.

The FAA had committed a significant

budget and many technicians to compound a jet fuel with a new additive

intended to prevent airplanes from

burning on impact. It was a wonderful

idea. It had passed the reviews, the

simulations, the small-scale demolition

rehearsals. But the real flight was different. Later, investigation would reveal the

unforeseen factor, a wing cutter slicing

through an engine on impact. The airplane

erupted in a giant fireball and burned for

an hour.

The unhappy project had flown under the

acronym CID, Controlled Impact Demonstration. Gilyard smiles, recalling that

wags on the base to this day explained the

acronym as “Crash In Desert.”

“It burned like a blowtorch,” recalls

Gilyard.14

* * *

Now Burcham had an informal team

assembled to work on PCA control laws

including two newcomers, Jeanette Le,

just graduated from UCLA, who would

function as the sim engineer, and Joe

Conley, fresh out of the engineering

program at the University of Illinois and

the NASA coop program, who would be

responsible for the analytics. Burcham’s

12 The acronym TOC is important to this history. It refers to the pilot manually operating the engine throttles to provide

flight control. The acronym later adopted, PCA (Propulsion Controlled Aircraft), refers to augmented controls the project

developed to help the airplane land.

13 Burcham, “Cleared for Landing,” 20.

14 Last section based on Glenn Gilyard, interview with author, 16 June 1998.

7
xiv

project had advanced beyond the four

corners of his desk to become a training

ground for two new-hires with a thriftshop choice for its testbed.

Late in January of 1990, Gilyard sketched

out the control laws. More than anyone

anticipated, the first effort looked very

good. Le brought up what had early-on

been a more-than-adequate 720 sim and

modeled it for flight using throttles for

flight-path control and other multiple

scenarios. Within a week, these engineers

were flying the PCA system in the sim

lab.

“No pilots involved at first,” winks

Gilyard, “no sense in embarrassing

ourselves, huh? Typically it takes months

and months if not years to get results.

Normally, you start at your desk; you

make a mathematical representation or

model of the aircraft. Then you do the

control law design at your desk. What we

did was the exception to the rule. We

jumped right into the sim.”15

A simulation is a software model of an

airplane. The model includes a maze of

subsystems, the propulsion system, the

control system, an aerodynamic model, an

actuation model, a model typically of a

specific airport and actual runway, models

of weather, wind, turbulence, gusts. In

effect, when you stepped into the plywood cockpit of the Dryden 720 sim, you

entered an elaborate video game, an

arrangement that might answer any

number of speculative questions about

flight but that at the same time entailed

none of the risks of real flight.

The 720 sim was rough. It was a plywood

box; it had only two throttles so that the

sim had to tie two software engines

together on the left and two on the right.

The video screen offered a tiny rectangle.

The mathematics of its models had been

derived for another project whose focus

was crashing, instead of not-crashing. Yet

the more sims Burcham saw, the more

certain he became that in some manageable way, thrust would do to land an

airplane.16

During these “quickie” formulations,

another issue arose. It was not part of the

propulsion control modeling. But it was

part of any safe landing in a catastrophic

scenario. The speed of the aircraft without

normal flight controls is mostly locked

into the speed flown before control was

lost. An aircraft has what is called its trim

airspeed, an inherent speed the airplane

attempts to maintain. Speed is only

peripherally affected by changing thrust.

To an outsider, it might seem that if you

want your car, for instance, to slow down,

you take your foot off the gas pedal. But

in the PCA mode, if you cut back on the

throttle, you do not decrease speed—you

pitch the nose down. Correspondingly, if

you bring up the throttle, you pitch the

nose up. The increases and decreases in

angle of attack cause drag which marginally affects speed, but you face a problem:

if you are flying at altitude at 280 knots

and experience catastrophic loss of your

normal controls, even when you engage

PCA, you still fly at something

unnervingly close to 280 knots. How do

you slow down to perhaps the 170 knots

needed for a safe landing? Here was an

issue to address. But as Gilyard, the old

control-law warrior, noted: his assignment

at this point was done, and the flight

demonstration was for others—it was, as

he phrased it, “another set of realities.”17

For the moment, the problem of trim

speed could be postponed. Burcham had

some promising results, and he needed

15 Gilyard interview.

16 Jeanette Le, interview with author, 24 June 1998.

17 Gilyard interview.

8
xv

Figure 7. Dryden

Director Ken

Szalai’s note to Bill

Burcham.

every bit of confidence he could get.

There were many naysayers on the topic

of PCA, and the roughest criticism came

from the nearest hallways. “This is just

plain stupid,” snorted one fellow engineer.

“Hare-brained!” echoed another aeronautical designer. A Dryden expert warned

him, “You are defying the laws of physics!” Skepticism was voiced from all

levels, low and high. The Planning

Council at Dryden did not offer funds.

“By the time you had brought it up to ten

people,” recalls Jim Stewart who shared

the early advocacy, “you almost hated to

bring it up.” Burcham’s logbook has

entries for many PCA briefings that

winter which end with the notation “no

interest.”18

Why were there so many doubters?

Perhaps one of the answers was cultural.

In this realm of specialized research, there

was a propulsion culture and a separate

flight control culture. PCA was a hybrid

of both that pleased traditionalists in

neither. And another factor surfaces too:

the whole concept of PCA was, in a large

way, unsettling. An engineer now sympathetic who prides himself on openness to

new ideas recalls that at first he did not

think the technology would work, “PCA

wasn’t intuitively obvious. The problem

hinged on this,” his eyebrows widen for

emphasis, “It was novel.”19

Early in the spring, Burcham received a

brief note from Ken Szalai, Director at

18 Frank W. Burcham, unpublished log books; Stewart interview. The Jim Stewart interview with the author was one of

the more extensive sources on early skepticism about PCA.

19 Tom Wolfe, interview with author 4 Aug. 1998.

9
xvi

NASA Dryden. Although it was informal,

casually scrawled by hand, the note

arrived as a real trumpet blast. “I want to

develop the propulsion-enhanced flight

control work as a NASA-led R&D

[Research and Development] program,

with strong in-house technical and

technology leadership,” he announced.20

Szalai did not offer him a budget or

people to stack against the project, but at

this stage, what he offered may have been

more essential. Szalai had received a

message from NASA Headquarters in

Washington, D.C. There was concern at

Headquarters that PCA might excite the

regulatory agencies before it had been

fully explored and create problems for the

aircraft manufacturers. “The advice I got

from Headquarters,” recalls Szalai, “was:

‘We’d prefer you not actually work on

this at all’—which was a stunning blow to

me.”21 Szalai chose to act as buffer rather

than a messenger. Burcham recalls, “My

boss ‘forgot’ to tell me this until several

years later.”22

Burcham flew most of the Boeing 720

sims. What was the next step? Burcham

needed to test the concept in actual flight.

Thus, he needed a real airplane and a real

pilot.

In March of 1990, Burcham paid a visit to

the pilots’ office. He ambled over to a

pilot at his desk. He asked, “What do you

think about using engine thrust for flight

control? Would you like to take a look?

How about flying a rough sim?” The pilot

was Gordon Fullerton.

Fullerton was in his early fifties then, a

graceful, athletic man with pale blue eyes

that could gleam with humor. His face

was burnished, even wizened perhaps

from thousands of hours of flying in the

fierce glare of the desert. Everyone on the

base called him Gordo, this ex-astronaut

and test pilot whose skills were the stuff

of legend.

Fullerton’s eyes glittered at Burcham’s

questions. Yes, he was definitely interested. Here was the man who had brought

the STS 51F Space Shuttle down at

Dryden willing to try to land a crippled

commercial liner—or at least the simulation of one.

In an instant in the hallways at Dryden,

PCA gained credibility.

It was some combination of curiosity and

the challenge that hooked Fullerton. He

followed Burcham to the plywood cockpit. Burcham mentioned that he himself,

after some practice, had accomplished a

successful landing using the throttles for

control. “How would you like to try?” he

asked.23

When Fullerton tried this unusual system,

he entered a new realm. Where normal

flight controls had done his bidding in an

eyeblink, even in simulation the big

lethargic engines might take what seemed

like an eternity to respond. It was waitand-see flying, a sort of dismaying

process of anticipation, especially because

the real-world situation would be one of

desperation. The pilot commanded; the

pilot waited. Later, one NASA test pilot

referred to this type of flying as “herding

a cow across the sky.”24

20 Kenneth J. Szalai, unpublished note, 14 Mar. 1990.

21 Kenneth J. Szalai, interview with Dill Hunley, July 1998.

22 Burcham, “Cleared for Landing,” 21

23 Burcham interview, 12 Aug. 1998.

24 Purifoy interview.

10
xvii

To a nonpilot, the comparison would be

driving on the freeway and having to turn

the steering wheel nearly half a minute in

advance of the vehicle’s response. A

phugoid cycle, for instance, lasts about 60

seconds and the thrust input to damp it

must be given more than 20 seconds

before there will be a perceptible indication that the input has had an effect. If the

pilot gives a command, then observes no

reaction, he may repeat the command and

overcorrect with damaging effect. Without flight controls, if the airplane noses

up, threatening to stall, the pilot will push

his throttles forward, the reverse of the

thrust input needed. In these last-resort

circumstances, Joe Conley points out,

“pilots will revert to natural instincts and

natural flying instincts will kill you.”25

Burcham’s insight, which dated back to

the sketch on the napkin, was that while a

pilot would find it impossible to stop a

phugoid with less than a 50/50 chance of

even nudging the thrust in the right half of

the oscillation, if a computer could help—

if it could receive responses from motion

sensors 40 times per second and react to

each with a tiny correcting, nearly imperceptible nudge of the throttle—the

airplane could be controlled.

Flying TOC (Throttles-Only Control) was

tough. But after five or six tries at the

sim, Fullerton mastered the task. His

technical curiosity may have weighed in

as one factor, but the larger factor was the

challenge. Ego in abundance is required

of flyers in his occupation. Test and

research pilots needed it to function,

given the risks involved. The risks were

real. If you look up at any street sign in

the numerous roads intersecting around

the Edwards runways, you see the names

of pilots who have gone down in fireballs

on the desert just beyond.

Fullerton had followed the Sioux City

incident as closely as Burcham. As a

research pilot who daily faced risk and the

potential for deadly surprise, he admired

what the pilots at Sioux City had accomplished. “What you guys did blew me

away,” he later told Dennis Fitch, the

airline check pilot who had come forward

that day from the passenger section to

work the throttles.26 In these early stages,

Fullerton brought an additional front to

the attack on the problem, one a bit

ignored since then. He sought to develop

a set of practical guidelines to help pilots

whose airplanes lost some or all flight

control surfaces.27

In addition to his willingness to evaluate

sim flights, Fullerton made another

contribution. He had noticed that some

guest simulation pilots had problems even

after the PCA was engaged. “One fighter

test pilot,” remembers a Dryden controls

engineer, “never did get the hang of it.”28

At first glance, the stick had seemed the

most efficient way to introduce and

control PCA. But in a catastrophe, the

pilot might expect the stick to respond

immediately as in normal flight. Fullerton

suggested putting the controls in

thumbwheels, the hardware typically used

in operating autopilots. Two thumbwheels

were added to the panel, one for dialing in

lateral commands, the other for longitudinal commands. Tests with more guest

pilots confirmed the decision. “The

thumbwheels,” says Jim Stewart, “put it

in the comfort zone.”29

25 Joseph Conley, telephone interview with author from NASA Ames, 19 June 1998.

26 Dennis Fitch, telephone interview with author, 15 July 1998.

27 Gordon Fullerton, interview with author, 7 July 1998.

28 Burken interview.

29 Stewart interview.

11
xviii

Another significant breakthrough came

from Joe Conley. As he worked through

landing data in analytics, he stepped back

mentally and asked himself if there were

some way to make his outcomes more

predictable. Burcham had conjectured

about using the ILS (Instrument Landing

System)—a radio-beamed tracking

system that helps guide actual airplanes

onto the runway in bad weather. What if

the inputs from ILS were added to the

inputs PCA used? Conley designed a

simple ILS and added it to the PCA sim. It

was a deft move. In terms of the sim, the

scheme was merely a pleasant improvement, but in a year, in terms of real

airplanes coming down onto the runway,

it played an important role.

Some PCA skeptics viewed Sioux City as

a once-only instance. “Why bother?” they

explained, “because it will never happen

again.” Burcham and Fullerton did some

research looking for other airplane

accidents that could be traced to lost

hydraulic controls. At first, the naysayers

were confirmed—nothing showed up.

Then one afternoon while traveling, Jim

Stewart gave a talk about PCA. Afterwards, an Air Force man came up to him

out of the audience. “I have to talk to

you,” he said.30

In 1975, an incident happened in Vietnam

to a USAF C-5 transport evacuating

orphans from Saigon. When a bulkhead

failed in the aft fuselage, all hydraulics to

the tail were lost. The pilots had flight

controls for roll but none for pitch. They

tried using the throttle and found that it

provided some pitch control, but were

unable to control a phugoid on approach

for emergency landing. The phugoid

caused the aircraft to crash-land into a rice

paddy. Of 314 passengers, 138 died but

176 survived.

In the months that followed, the Dryden

searchers discovered other incidents. In

1985, a Japan Airlines flight suffered total

hydraulic loss. Out of control, the airplane

flew for 30 minutes before hitting a

mountain, killing 520 people. The same

year as the Sioux City crash, a Navy

fighter flying over Jasper County, Indiana,

lost hydraulic controls, and when the

aircraft rolled off uncontrollably to the

right at an angle of 90 degrees, the pilot

ejected. Another crew on a commercial

flight near San Diego found the airplane

about to stall in an uncontrollable pitch-up

when they used throttle controls, changed

pitch by thrust modulation, and landed

safely. A 1974 flight departing Paris was

less fortunate. The airliner lost some flight

controls, diving into the ground at high

speed. All 346 aboard perished.

It was grim arithmetic but was part of the

factoring needed to convince an industry

and its regulators to look seriously at

PCA. As other accidents came to light, the

Dryden researchers assembled a list of

relatively recent incidents involving more

than 1,100 fatalities.31

* * *

One of the guest pilots in the spring of

1991 was Al Haynes, captain of the Sioux

City Flight 232. During the year after the

crash, he began to give an inspirational

30 Stewart interview.

31 Cf. Frank W. Burcham et al., Development and Flight Evaluation of an Emergency Digital Flight Control System

Using Only Engine Thrust on an F-15 Airplane (Edwards, CA: NASA TP 3627, 1996): 2-5, and Military Airlift Command History Office, Anything, Anywhere, Anytime: An Illustrated History of the Military Airlift Command, 1941-1991

(Scott Air Force Base, IL: HQ MAC, 1991), pp. 152-153.

12
xix

Figure 8. Al Haynes

in the Boeing 720

simulator with (left

to right) Gordon

Fullerton, Bill

Burcham, and Jim

Stewart. (NASA

photo EC91-316-2

by Bob Brown).

speech around the country regarding

cockpit resource management and emergency preparedness. He came to Dryden

and spoke to an overflow audience.32

Afterwards Burcham and Fullerton took

him to see the 720 sim, but when they

invited him to fly it, he turned them

down.

Here was unexpected resistance. This

pilot had been rock-steady during his

ordeal. In audiotapes of his remarks to the

Sioux Gateway control tower, there was

not a crack in his voice as Haynes announced as casually as if he were talking

about weekend recreation plans, “We’re

not gonna make the runway, fellas.”33

But this was different. He hesitated;

perhaps his eyes moistened.

“I don’t think I want to fly the simulation.”

“Why?” asked Fullerton.

“I don’t know . . . to get back in a cockpit

faced with the same situation.”

He stared a moment at the dim contraption. But he did get in; he flew the sim

later that afternoon. He punched the PCA

button, approached the runway; PCA

eased him to glideslope, and the gray

runway on the video screen came closer.

On his first effort he was able to put the

plane safely on the ground.

Al Haynes was pleased.34

32 Al Haynes, interview by telephone with author, 16 June 1998.

33 Al Haynes, from video accompanying speech, “The Crash of Flgt. 232,” 24 May 1991.

34 Most of the Haynes and simulator story come from the Gordon Fullerton interview.

13
xx

* * *

Burcham’s idea was big. It was big in the

unexpected ways it kicked in sometimes

more strongly than the engineers had ever

predicted. Bill was the first impetus

behind the project, but PCA was much

bigger than any one individual, and teams

would form and reform, members dropping in and out, one person making some

significant, defining contribution, then

another. At the NASA center best known

for supersonics, this subsonic idea lumbered along with the speed of a transport.

It survived, moving through an institution,

through units and sub-units, a bit of a

stealth project because it had no budget to

be shot down, moving through “mature

technology,” moving through an

engineer’s off-time on Saturday afternoon, through carpool debates, reviews,

briefings. And PCA was about to

reconfigure with another unit that would

help it survive, the U.S. Air Force.

Burcham was looking for funds. He could

not “buy” an airplane, but he needed to

buy a feasibility study, to look at how to

prove the PCA concept, how to

reconfigure a real airplane with this

technology. The Air Force’s Terry Neighbor from Wright-Patterson Air Force

Base, who headed a group investigating

controls integration, had listened to

Burcham pitch PCA to another Air Force

unit, which ultimately expressed lack of

interest. Neighbor did find PCA interesting. He recalls it as “another dimension of

something we were doing.” Neighbor

went back to his office, got his hands on

some managerial discretionary funds,

initially $100,000, which in the scheme of

more visible projects was pocket change,

but which for PCA was a vital infusion,

the funds needed for a feasibility study on

the project’s first real airplane testbed, an

F-15.35

NASA Dryden had an F-15 in the hangar

at Edwards. The F-15 is a high-performance fighter airplane from McDonnell

Douglas Aerospace.36 What attracted

Burcham was that this Dryden F-15 had

two computer systems, a digital flight

control computer, FCC, and digital

electronic engine controls, DEEC. These

two systems can “talk” to each other, and

both are programmable. Earlier projects—

most recently, HIDEC—had already

loaded Dryden’s F-15 with expensive

testing instrumentation. Despite these

attractions, among all the airplanes in the

world if the researchers had been given a

choice, the F-15 would have ranked

among the last.

The problem was the engines. They were

two big, powerful turbofans relegated to

the rear of the airframe. A mere 12 inches

separated the two brutes, and if PCA

technology depended on differential thrust

between the right and left engines, how

would the F-15 respond? Some rough

sims had looked encouraging, but sims

were sims, and the robust power of flight

control surfaces might have masked the

effects of the closely spaced engines.

The study was contracted to McDonnell

Douglas Aerospace in St. Louis, Missouri.

New faces now appeared on the team.

McDonnell’s Jim Urnes became project

manager for the task and Ed Wells was

design and flight test engineer. Now trips

to simulators took Burcham and his

colleagues to the spectacular F-15 simulation in St. Louis. It was a real F-15

cockpit with real F-15 controls, and

35 Terry Neighbor, interview by telephone with author, 4 Aug. 1998.

36 Today, the companies mentioned in this history are all part of Boeing. But in these pages, they will be designated as

they were then separately known for most of the duration of the PCA work. They included McDonnell Douglas Aerospace in St. Louis, which did PCA studies for the F-15; McDonnell Douglas Aerospace Long Beach, which did PCA

studies for the MD-11; and Douglas Aircraft Company operating the MD-11 out of Long Beach and testing in Yuma.

Boeing was a separate and independent company headquartered in Seattle.

14
xxi

dramatic scenery wrap-around on the

inside of a 40-foot dome. If Burcham had

an hour remaining at the end of a day

devoted to the big HIDEC project, he ran

a PCA test.

Safety features designed into the sim

were the ones to be designed into the real

airplane. All modifications were software

ones—with one exception, the addition of

a cockpit controller for PCA. The hydraulics were never turned off. The pilot used

the emergency mode of the mechanical

flight control system, which did not have

the flight control computers automatically

driving the control surfaces. At the

slightest touch to stick or rudder pedals,

the pilot could engage the normal flight

control surfaces.

Dryden’s Tom Wolf introduced many

modifications to the Dryden F-15 sim to

account for the new F-15 configuration.

Ed Wells, the St. Louis F-15 specialist,

added these control laws to the

McDonnell sim and customized the 720

version of the flight control laws for the

F-15.

Hardware arose as an issue. Fullerton had

voted for thumbwheels as the controllers

of choice, but McDonnell decided the

question needed systematic review. And

the thumbwheels posed a problem:

McDonnell had a thumbwheel panel from

an F-4 Control Configured Vehicle (CCV)

program that was qualified only for lab

use. The researchers did not have a flightqualified unit to install in a real airplane.

Jury-rigging knobs for a sim was one

thing but installing hardware not certified

for flight was another. “Our shoestring

program did not have the funding for

designing or building new ones,” remembers Burcham. McDonnell framed four

options for the study. These included the

central control stick, a ministick springloaded and moved by force, another

spring-loaded ministick moved by degrees, and the F-4 CCV thumbwheels.

Each option had negatives, and a series of

guest pilots flying the sim again decisively confirmed the wisdom of the

thumbwheels.37

Where to get the flight hardware? At this

point, the Air Force came to the rescue,

Figure 9. Gordon

Fullerton and the

two “brutes”

(engines) in the F15 after he had

landed the aircraft

using only engine

power for control

on 21 April 1993.

(NASA photo

EC93-41034-3 by

Larry Sammons).

37 Burcham interview, 17 June 1998; Edward Wells and James Urnes, Design and Flight Test of the Propulsion Controlled Aircraft (PCA) Flight Control System on the NASA F-15 Test Aircraft (Edwards, CA: NASA CR 186028, Feb.

1994): 9-11.

15
xxii

and Major Bob Yeager, who had joined

the PCA team, tracked down the

thumbwheels still in an F-4 CCV resting

in a flight museum in Dayton, Ohio. He

talked the museum into loaning the

thumbwheel panel; herded the curious

transaction through stacks of paper

regulations; and for the life of the project,

the F-15 sported flight-qualified

thumbwheels.

It was clear from the beginning that the

team would need to perform actual flight

tests of PCA. Some engineers say that

flight tests are not needed when a good

simulation will suffice. But PCA itself

was so new, so different, that many

questions arose. The test to provide

answers to these questions would take

place up in the air.38

The first dedicated throttles-only control

flight test arrived the morning of 2 July

1991. In the summer, Dryden flight

research often starts at the crack of dawn

before the thermals produce strong

updrafts. Sometimes the hangar crew

begins as early as 2 a.m. These moments

have a curious look—the operations area

is a world of metal and certainties but at

that sleepy hour displays all pastel colors,

the desert sky before sunrise, a pale

Easter-egg blue, and the airplane glimmering softly like a reflection. Fullerton

strolled out to the F-15 with his test cards

clipped to his sleeve, ready to take this

project to the next stage. But although the

team had anticipated some problems,

although they had replaced one engine

with an identical mate to the other, they

were not prepared for what happened

next.

The flight did not go as planned. Fullerton

took off in the sleek fighter and then

brought the F-15 up to altitude to begin

following his test cards. He set up the

airplane for TOC and in the instant joined

the brotherhood of Haynes and Fitch at

Sioux City: no ailerons to control airplane

roll; no elevator to dictate pitch; no rudder

to yaw a turn at command.

All Fullerton had was his hand on the

throttles and even before he moved them,

strange things began to happen. “I was

looking at the sky and then the dirt and all

over,”39 he remarked. When he tried a

gentle pressure to correct pitch, the

airplane entered a roll. He reacted. He

throttled to stop the roll. The F-15 responded by pitching down, then up,

seemingly with a mind of its own.

What had happened? In mid-air, in an

instant, Fullerton guessed at a part of the

Figure 10. Threeview drawing of an

F-15 airplane.

38 Fullerton interview.

39 Gordon Fullerton, from transcript of interview with Lane Wallace, 7 Sept. 1995.

16
xxiii

Figure 11. Diagrams showing the

early F-15 simulation versus actual

flight in the F-15 in

manual, throttlesonly approaches at

170 knots with the

flaps up and the

control augmentation system off.

answer. In the simulation, the mathematical model had provided him with two

perfectly identical engines. But they were

just models. Even “identical” engines had

slight differences. When control surfaces

operated, these minimal differences had

no effect. They were masked by the power

of the flight controls. But when you

turned the normal controls off, the big

engines, with a little nudge, did big deeds.

Because one engine spooled up to full

throttle sooner than the other, every input

sent the F-15 careening across the sky.40

When Fullerton brought the airplane

down the glideslope to the runway, he did

so with normal flight controls turned on

and at the moment of touchdown, the one

proof of the day might have seemed to be:

you can never land an F-15 airplane

safely using throttles-only control. The

faces above in the control room had a

40 Fullerton interview.

17
xxiv

Figure 12. Bill

Burcham and

Trindel Maine at an

F-15 simulator

session. (NASA

photo EC95-43026-

2 by Jim Ross).

stricken look. And surely in the hallways,

the naysayers were nodding ‘I-told-youso.’

“Humbling” is the word Fullerton uses in

summation; “it’s a matter of pride. I can

do anything. This airplane’s not going to

get the best of me. And it did. It really

did.”41 When the F-15’s flight controls

were turned off, the airplane became

aerodynamically very unstable, what

Fullerton called a “squirrelly airplane.” As

far as his colleagues could tell, Burcham

appeared unfazed. But he trudged to his

car with a stack of test data printouts, and

it was only Tuesday night. Usually, he

waited until Friday night to bring them

home. He would have the long drive

across the bleak desert to ask himself

questions. Why was the F-15 sim so

different from the real airplane? As one

associate said, “When Bill started to deal

with these propulsion effects and effects

near landing, there weren’t any guidelines

to help him . . . he was going to have to

write the book.”42

* * *

The team set about making major modifications to the F-15 sim. If the sim was

improved, they should be able to duplicate what Fullerton had seen in actual

flight. In the first days, they realized that

the F-15’s center of gravity (CG) shifted

as the fuel was consumed, and the

airplane’s weight and weight distribution

changed. They modeled the sim to

incorporate this data. The F-15 went to a

second flight test, but the results remained

poor. Fullerton could maneuver somewhat

up and away, but the F-15 without control

surfaces was an unstable airplane. He did

not have anywhere near enough control

for a safe landing. When he pushed the

collective throttles up, the airplane rolled.

41 Fullerton interview with Lane Wallace.

42 Burken interview.

18
xxv

Figure 13. Features

of the PCA system

on the NASA F-15

HIDEC airplane.

A series of tests followed, flights, sims.

Some of this process was “tweaking” and

“de-bugging.” The team had larger,

shadowy factors to discover, and one of

them turned out to be inlet effects.

Trindel Maine, a Dryden engineer who

joined the team at this stage and had a

reputation as a wizard at scanning data

sheets and spotting a trend, saw the

process for what it was. A daunting

number of factors come into play when an

airplane maneuvers with throttles, and the

researcher at last brought this one to light.

The big, overhanging ramp-air inlets are

beside the pilot. It turned out that when

Fullerton wanted the nose to drop and

pulled the throttles back, the reduced

airflow to the engines pushed up on the

inlet ramps and raised the nose. This

effect is normally masked by the pilot’s

commanding a minor change in the

elevator position, but with no elevator

movement, the inlet effect caused the

airplane briefly to pitch in the wrong

direction. The Dryden and McDonnell

team developed a model of the inlet effect

and added it to their simulations at

Edwards and St. Louis. Now the TOC in

the F-15 sim went up a notch in difficulty

but still did not match the flight research

data.

Another problem involved the ground

effects. “Ground effects is a black art,” says

Trindel Maine; “we just don’t have any

good ground effects models out there.”43

Some ground effects studies do exist, but

they are based on fixed throttle settings and

are not well modeled. Normal flight

controls operate so powerfully, they mask

ground effects. When the F-15 came within

a wingspan of touchdown, it entered this

realm of unruly aerodynamics.

The engineers needed ground-effects data

that were non-existent. “This was an area

where the simulator model was suspect

. . . where we were quite concerned about

knowing what we’d be dealing with,”

explains Maine. The team commissioned

a study addressing ground effects on F-15

landings.44 The study was conducted in

the traditional fixed-throttle setting and,

as a consequence, did not match very well

what the team encountered afterwards in

PCA flight. “The final answer didn’t

become clear until much later,” Maine

43 Trindel Maine, interview with author, 2 July 1998.

44 See Stephen Corda et al., Dynamic Ground Effects Flight of an F-15 Aircraft (Edwards, CA: NASA TM 460, June

1994).

19
xxvi

Figure 14. Gordon

Fullerton climbing

aboard the F-15 for

the 21 April 1993,

research flight.

(NASA photo

EC93-41034-4 by

Larry Sammons).

remarked. “. . . the PCA control laws

moving the throttle actively during the

landing phase had a big impact on how

the ground effects actually affected the

flight path.” As it learned more about

ground effects, the team worked to

minimize the most severe effect, an

alarmingly high sink rate just before

touchdown.45

In addition, the engineers modeled the

sims more closely to the Pratt & Whitney

engines, identifying lags and rate limits.

They put modeling in the sim for landing

gear and its actual effects on aerodynamics. Gyroscopic movements from the

powerful engines were factored in. But

despite all these efforts, flight difficulties

persisted.

“Some unmodeled effect was obviously

present,” said Burcham. The team had not

solved this mystery, but it hoped that the

computer and the feedback sensors of the

PCA system would be able to accommodate the problem. “It was time to see,” said

Burcham, “if the PCA system—with the

computer taking the pilot inputs, factoring

in the sensor feedbacks, and figuring out

where to put the throttles—would work.”46

In the early weeks of 1993, Fullerton

conducted the initial flights with the PCA

system engaged. PCA showed much

improvement over TOC, but still presented

some problems. The noisy signals from

some of the sensors required filtering, and

bank angle feedback was needed. Fortunately, back in an earlier design review,

45 Maine interview.

46 His comment on a draft of this narrative.

20
xxvii

Figure 15. Gordon

Fullerton and Bill

Burcham next to

the F-15 aircraft.

(NASA photo

EC93-41034-11 by

Jim Ross).

Glenn Gilyard had noticed that the bank

angle was not one of the feedback sensors

and had it added. Ed Wells had introduced

flexibility into the test process by making

available points in the software where the

pilot could select variable gains, filters,

multipliers, and gain schedules. It provided a quantum leap. The researchers

could carry on real-time dialogue over the

radio with the pilot and alter PCA. It was

working fast—it was depending on a

small team of highly skilled individuals.47

With the changes, the team improved

control enough to try low approaches to

the runway.

Many standards apply to landing an

airplane. Some resolve to this question

during a commercial aircraft landing:

would your coffee stay in its cup (assuming the flight attendants had not collected

cups before landing, as they normally

do)? But others resolve differently: do

you walk away with your life? PCA is

47 Jim Urnes, interview by telephone with author, 26 June 1998.

21
xxviii

Figure 16. Threeview drawing of the

McDonnell Douglas

MD-11 research

airplane.

defined by catastrophic alternative. In

fact, later, PCA had the robustness to

make landings so smooth they were

difficult to distinguish from normal ones.

On the morning of 21 April 1993, however, when Gordon Fullerton flew the F15 on the downwind approach to

Edwards’ runway, he did not have the

word “gentle” in his pilot cards. He used

the PCA system for a series of approaches

at altitude at different trim speeds, and

then he brought the F-15 down near

ground level. “When we flew within 10

feet, we knew we had success,” recalls

Jim Urnes, the McDonnell project manager.48

On the next flight, Fullerton made aeronautics history when he flew the first PCA

landing. He descended in a very shallow

approach to 20 feet above the ground;

then his sink rate rose quickly to 8 feet

per second. The unfazed Fullerton,

however, remained confident and brought

the F-15 to a “firm but acceptable”

touchdown 6 feet left of the runway

centerline. “Smoke flew off the tires,”

remembers Urnes.49 Nevertheless, the

system had landed an airplane.

The system might not pass the coffee-cup

test. But it could get you safely down.

“It was like landing on the moon,” recalls

one project manager about the applause

for the F-15 landing that erupted in the

Dryden control room and echoed around

the industry for weeks to come. “Look Ma

No Hands” trumpeted Aviation Week &

Space Technology.

50

In a real disaster, PCA would be the

technology of last resort for first-time

users. The team addressed this issue after

the F-15 landings, when it invited six

pilots unfamiliar with PCA to test approaches and go-rounds. All the pilots

flew the system successfully and were

enthusiastic about PCA’s capabilities.

“Pitch control was awesome,” said Navy

Lieutenant Len Hamilton. He indicated

that he would rather have PCA than the

backup control technology in his current

F-14.51

48 Urnes interview.

49 Ibid.

50 See Michael Dornheim, “Industry Outlook: Look Ma, No Hands,” Aviation Week & Space Technology (3 May 1995): 11.

51 See Appendix D for guest pilot remarks at greater length.

22
xxix

The engineers, pilots, managers, all of them

had understood one brutal point about the

industry position: until you proved this

technology on a small airplane, you had no

chance of getting on a big airplane. Now

that they had proved it on the F-15, the next

airplane waiting for PCA was the MD-11.

The MD-11 is a widebody transport

airplane that succeeded the earlier DC-10, a

huge three-engine vehicle more than twothirds of a football field in length. The MD11 with its full flight control autoland

system, its digitally controlled engines, and

fully integrated design was a next-generation aircraft, the type of aircraft that was in

the cards from the day the idea was

sketched on the napkin.

Even before the historic PCA landing of the

F-15, efforts were made to arrange PCA

experiments on a large transport airplane.

One crucial moment occurred during a

meeting at NASA Headquarters in Washington, D.C.

In December 1992, Dwain Deets, then

Acting Director of Dryden Research

Engineering, attended this pivotal Headquarters session. Assembling around the

conference table were executives from

every big player in aircraft manufacturing

and also the directors from the other NASA

centers. Bob Whitehead, Director of

Subsonic Transportation in the Office of

Aeronautics and Space Technology at

Headquarters, convened the group. Szalai

had asked Deets to attend and represent

him, and Burcham attended as technical

support.

Deets had spent many years as a Dryden

spokesperson in Washington, D.C., meetings. He recalls a sense that day of venturing into hostile territory. The issue was

endorsement. Whitehead would not let the

centers proceed on a project unless they had

industry endorsement. From the start,

Boeing had been very cool to the idea of

PCA. Whitehead was not looking for mere

industry neutrality. “Whatever it is we do,”

he was quoted as saying, “it’s got to buy its

way onto the airplane.” Another concern for

Deets was NASA Langley, the center that

specializes in subsonics. Burcham and his

colleagues were venturing on Langley turf.

Burcham had already briefed Langley about

PCA and had not been well received. In the

future of this technology, there would arise

remarkable cooperation between Langley

and Dryden. But at that time, observers

recall, jealousy was often the norm between

centers. And it did not help that a series of

recent promotions to Headquarters had

gone to Langley execs, many of them

advisors to Whitehead.

Whitehead, however, when he opened the

meeting spoke favorably about PCA. He

was brief; he did not cajole, debate, or

insist; and Deets had the distinct sense of

watching a referee toss a ball into play at

the start of a contest. When his turn came,

Deets gave the briefest of presentations—

everyone at the table knew what the issue

was. Next, the floor moved around the table

from one executive to another. John King,

from McDonnell Douglas Aerospace in

Long Beach, gave an extremely strong

endorsement. So did NTSB member John

Lauber. Finally, came the turn for the man

from Boeing.

“I never saw anything like it,” Deets

remembers today with a touch of wonderment. “He didn’t say anything. Everyone at

the table had their eyes fixed on him. It all

hinged on this moment. But he didn’t say a

word; he just glared down for quite some

time, the room utterly silent, and then he

made a quick movement; he made this

thumbs-up sign. That was all, that was that

. . . it was a done deal.”

The meeting moved quickly to other items

on its agenda. When Deets and Burcham

returned to Dryden, they brought home

good news.

“It’s a go,” they said.52

52 Dwain Deets, interview with author, 1 July 1998.

23
xxx

The MD-11 experiment was destined to be

much more successful than the F-15. But

the crises to be faced were different and

these had nothing to do with harrowing test

flights. The crises occurred in well-cushioned conference rooms. Now the project

had a $2.5 million budget line per year

resulting from the advisory meeting in

Washington. Now there were contracts,

subcontracts, and work orders rather than

reliance on the good nature of an engineer

at the end of a long day. And there was the

assignment of a project manager from

NASA Dryden, first Russ Barber, then Bob

Baron, and finally Joel Sitz ably guiding the

project through NASA internal processes.

Dryden engineers now included Trindel

Maine, John Burken, and Burcham, and

meanwhile Fullerton invited another NASA

pilot, Dana Purifoy, to join in the flight

research. New faces appeared because

McDonnell Douglas Aerospace in St. Louis

had developed the F-15, but the Douglas

Aircraft unit in Long Beach and Yuma had

the MD-11 under active development. The

project assembled talented test pilots John

Miller and Ralph Luczak as well as Walt

Smith for simulation studies. The remarkably ingenious engineer Jeff Kahler was

sent by Honeywell to install the PCA

software in the flight control computer it

had manufactured. During these early days,

GE and Pratt & Whitney, manufacturers of

engines slung on MD-11s, sent engineers to

the meetings. It was anyone’s guess what

engines would be attached when they at last

found their specific testbed.

The MD-11 sims developed nicely. “You

sure you guys turned the button off?” asked

one guest pilot, a comment that was

repeated for months. But although flight

controls were turned off and PCA engaged,

something else subtly was turned off.

Months passed; an inertia began developing. One resident expert from McDonnell

admitted off the record, “This scared me to

turn off all the traditional flight controls.”

Burcham had shepherded the PCA into a

new environment. At his own desert lab,

debate had been informal, personal, and inyour-face. Douglas Aircraft was corporate,

pleasant, and polite. A subtle transition had

been made—he was no longer an associate

but a client.

“The project had some difficulty,” remembers Russ Barber, “in transitioning from sim

studies to airplane modifications and

operations. We kept going down to Long

Beach for reviews and we kept getting more

and more sims.”53 Burcham does not like to

talk about the period.

What was the problem? It was, in the end,

economics. None of the commercial airline

manufacturers will specify a sticker price on

their wares. But when you see a jumbo

jetliner on the runway, you may be looking

at as much as 150 million dollars. Who

would lightly take such an expensive

product and, in terms of safe flight, go

backwards? Who would risk it? Burcham

had at last gotten a budget for PCA, but

within the parameters of the industry, he

was still on a shoestring.

Although Douglas produced MD-11s, it did

not own a single one. The firm did not keep

its 150-million-dollar product on the shelf

as if it were retail. The issue became: could

Burcham get an airplane?

Burcham himself had worn the project

manager hat whenever needed; his new

Long Beach technical associate, John

Feather, played that role now in a part-time

capacity. In addition to engineering duties,

Feather filed applications and attended

reviews in efforts to find a real airplane. But

all negotiations proved fruitless. At this low

point, even as Burcham spent hours on the

phone, in his phrase “going round and

round,” he at last talked Douglas Aircraft

into appointing a full-time project manager.

The man appointed was Drew Pappas.54

53 Marvin R. Barber, interview with author, 18 June 1998.

54 Frank W. Burcham, interview with author, 17 June 1998.

24
xxxi

“When Drew came on,” recalls Russ

Barber about the first week in June, 1994,

“almost overnight it turned around.”55

Pappas is a short balding man with a dark

mustache who insists on modesty. “I was

along to carry the bags,” he says. But as

many elements fell into place at his touch,

it became clear Pappas knew Douglas

Aircraft very well. He knew how things

got done, where the procedural gears

turned, how to keep the regulatory

process from jamming. “I have a Mr. FixIt mind,” he grins. “When I don’t know

what to do, I try to get the answer and fix

it.” He dismisses what he does as

“mother-henning,” and he sees himself as

a professional worrier, the detail-cruncher

along for the ride with genius.56 Within a

relatively short time, he found them an

airplane, the testbed, the MD-11. He

mother-henned a 150-million-dollar

airplane onto the runway.

The project regained momentum, confidence returned, but a surprise awaited

Pappas. Doubts about PCA still troubled

some of the most distinguished members

of his team. One afternoon at a simulation

in Long Beach, two colleagues spoke up.

These men had flown TOC and knew it

was rough. They anticipated two problem

areas: the degree of complexity in the

landing and the design of software to

handle the challenge of actual flight. PCA

technology might never work, they

warned.

Pappas recalls driving home stunned

afterwards. Now the questions whirled in

his mind. The implications began to settle

in. He wondered if the doubts voiced by

his team members would become a “selffulfilling prophecy.” He hesitated before a

step both unpleasant and risky. “What if I

requested changes in personnel?” he

asked himself. “Are these guys going to

kill my project, or worse, are they right?”

By the time Pappas pulled in the driveway at home, he had reached a decision.

He would request no roster changes; he

would re-focus his own horizons. “My

objective,” he explains, “was not to

achieve success, but to determine if the

task was feasible.”57

Flight 232 pilot Al Haynes had raised an

issue after he enthused about PCA. How

do you reduce the speed of the airplane?

During this stage, the engineers found the

answers always proved specific to the

airplane. Some airplanes have electronically-commanded stabilizers which, even

with hydraulics failed, will reduce speed.

Others have electrically or pneumatically

operated flaps that drop and reduce speed.

Moving the center of gravity to the rear of

the airplane can also reduce speed.

Lowering the landing gear slows the

airplane—the open wheel wells and

hinged landing gear doors produce drag.

Many factors were found to influence

airplane speed.

Douglas Aircraft introduced numerous

safety checks and procedures into these

experiments. In fact, at first only one

engine flew PCA in actual flight. But on

the historic date of 27 August 1995, when

Flight 221 went up over Yuma with both

engines PCA-equipped, the system once

again showed its surprising capability.58

The pilots took the airplane to 10,000 feet

altitude and turned the PCA system on. It

performed as smoothly as a normal

55 Barber interview.

56 Drew Pappas, interview by telephone with author, 17 July 1998.

57 Pappas interview.

58 The designation “Flight 221” does not refer to the number of research flights in the PCA program. Rather, the

number designates the flight in the total series of test flights performed by the specific MD-11 on any number of projects.

25
xxxii

autopilot, holding the wings level, controlling flightpath to a few tenths of a degree,

maintaining altitude to within plus or minus

20 feet. As his eyes moved over the panel in

the cockpit, safety pilot John Miller became

a convert. “On the first attempt, I understood the capability of the engineering team,

and they had done a fantastic job.”59 Miller

proved a powerful advocate for the most

compelling proof, a real MD-11 touchdown,

and it was Miller who begged landings and

other test envelope expansions from

Douglas management.

As the MD-11 tests had moved to lower

altitudes that August, the thermals—

updrafts off the blazing Arizona sands—had

begun to pose a significant challenge,

especially in the afternoons when temperatures soared to 115 degrees. Kahler and

Burken had worked feverishly to develop

control law changes to improve PCA’s

tolerance to gusts and thermals.

On 29 August 1995, the MD-11 made its

first PCA touchdown. The day started early

at the Douglas airfield in Yuma. “The crew

brief was at 4:30 a.m. in Yuma,” recalls

Burcham, “with takeoff just as the sun rose

over the desert mountains.” With the

modified software installed, the engineering

crew and pilots flew north that morning.

Their destination was Edwards Air Force

Base, with its vast natural landing site

adjacent to Dryden and the main runway at

Edwards where they would land. It was

home in a sense, marginally more forgiving

than Yuma in thermal intensity, and definitely friendlier in the length and width of

its runways. At Edwards, Fullerton completed successful approaches to 100 feet, 50

feet, and 10 feet above the runway. As he

finally approached for actual landing, the

thermals began to buffet the airplane, yet,

Burcham recalls, “Fullerton’s approach

looked good.” The pilot left the flightpath

command at -2 degrees, working the

heading knob. At 100 feet he made the

flightpath shallower, and the airplane came

down smoothly at a sink rate of 4 feet per

second on the centerline. Here was all the

promise of the F-15 flights delivered home

now in the landing of a commercial airliner.

The videotape records it: the vast bird

descending with all control surfaces

motionless, an exhilarating but eerie sight.60

Figure 17. Pilot

views of MD-11

performing a PCA

Instrument Landing

System-coupled

approach and

landing.

Figure 18. MD-11

touching down for

the first time under

engine power only,

11:38 a.m. August

29, 1995, at

Edwards. (NASA

photo EC95 43247-

4 by Dennis

Taylor).

59 John Miller, interview by telephone with author, 19 June 1998.

60 Based on a description of the landing written by Frank W. Burcham on the original draft of this account.

26
xxxiii

On 29-30 November 1995, landings at

Edwards demonstrated an improvement

dating back to Joe Conley’s inspiration,

the addition of ILS coupling to PCA’s

arsenal of signals. Kahler connected the

PCA and ILS software in the Honeywell

computer on the MD-11. The result

brought improved control to PCA and did

not require additional emergency-procedure training for pilots. Kahler also added

an autoflare to PCA’s arsenal for these two

landings, an improvement that demonstrated a feasible step toward “hands-off”

emergency touchdowns.

In the fall of 1995, two dozen guest pilots

from the major powers in commercial

aviation were given the opportunity to

operate PCA on the MD-11, flying an

ILS-coupled landing to 100 AGL (100

feet above ground level) before initiating

go-round.61 The pilot comment cards

Figure 19. Research pilot Gordon

Fullerton, project

engineer Bill

Burcham, control

engineer John

Burken, McDonnell

Douglas’ John

Feather, and

McDonnell Douglas

project engineer

Drew Pappas

emerging from the

MD-11 at the NASA

Dryden ramp after

the first PCA

landing in the MD11. (NASA photo

EC95 432351-3 by

Tony Landis).

61 See Appendix F for remarks from the two-day guest pilot session.

27
xxxiv

thundered with wonder and praise, but

beyond the hurrahs from demonstration

and experiments was another experiment

sometimes overlooked.

* * *

The ultimate test for PCA would be to

turn off all the hydraulics. The flight tests

had locked down all the surfaces, the

ailerons, the rudder, the flaps, but in a real

catastrophe, the surfaces would float to

some position. Would it be a good position or a bad one? The sims had made

predictions, forecasting a rather benign

pitchover to a higher trim speed. The truth

was uncertain. To turn off all hydraulics

might start a deadly scenario. What was

the worst that could happen? The result

might be what the engineers call a

“hardover,” a dramatically asymmetric

position, and because the ailerons creating

it have a more powerful effect than engine

controls, the engines could not power the

MD-11 out of it.

Burcham saw it as a crux issue. John

Miller brought something close to the

physical courage he used in test piloting

to the task of pleading this case. To the

shock of all involved, he convinced

management. Douglas gave them the goahead.

It was to be an ultimate test at the human

level, too. On MD-11 flights, the engineers traveled at the rear of the airplane,

sharing the risk that typically pilots faced

alone. Observers at Douglas still speak

with awe about the engineering team that

pored over test displays and made significant changes in flight to gains and lags via

intercom conversation with the pilot.

Some projects might take three weeks to

arrive at the same results. Some engineers

might spend whole careers working on

projects that never took them outside the

laboratory.

 “It was a bit eerie,” recalls Joel Sitz,

Dryden project manager when he remembers the change from dealing with PCA as

paper and reports to actually being there.

The vast hollow plane stretched dimly

into shadow, no seats, no carpet, no

paneling. As the pilot flew TOC, Sitz

could feel the airplane’s shuddering, “hear

the big engines slowly revving up on one

side and dying down on the other.”62

“Hey, this is what test pilots do every

day,” John Burken remembers thinking

when he peered out the MD-11’s cockpit

windows. As an engineer, he realized,

“you get numbed—and probably you

shouldn’t.” Burken has a sharp memory

of summer turbulence over Arizona. “It

was a very hot day, Yuma in August,” he

recalls. “The engineers were at the

monitors in back and the monitors were

rocking back and forth. One man was

turning greener and greener.”63 During

these experiments, one engineer attached

to the project refused to go up on the

flight tests, and once when he was scheduled, anxiety so overwhelmed him that he

became physically ill and checked into a

hospital. But at the personal level, he too

reached his small triumph — eventually,

he went along on a research flight.

After the successful landing in August,

Dana Purifoy substituted for Fullerton as

research pilot and in September flew the

MD-11 to an airspace over the Pacific the

pilots call “Whiskey Area,” an emptiness

where few commercial airliners fly and

where pilots are able to do freeflight with

few air-traffic-control constraints and

with no compromise. Here after tests of

PCA engagement at altitude and tests on

center-of-gravity issues, the crew completely shut down two hydraulic systems.

The airplane’s control surfaces assumed

an asymmetric position, and trim speed

increased. But PCA still dominated with

rough control. The final step in these

62 Joel Sitz, interview with author, 18 June 1998.

63 Burken interview.

28
xxxv

investigations, however, did not come

until two months later when Fullerton

returned to flight over the desert beyond

Edwards.64

In November, Fullerton took the MD-11

on a flight out over the Mojave to test

PCA with absolutely no hydraulics. For

Burcham, this trip was ultimate. He

himself always downplays any humanitarian angle, insisting that the crash of Flight

232 at Sioux City is a mere locus in the

chain of events, but the evidence is, Flight

232 is a benchmark. When the MD-11

tests were arranged, Burcham had the

engine at the tail pulled back near idle and

the two wing engines provided thrust

control, the very configuration of Flight

232. As the technology developed,

Burcham went out of his way to invite

pilots Dennis Fitch and Al Haynes to try

out PCA in simulations at Dryden and

Ames. When any guest pilot went up,

Burcham first handed the flier the situation that existed in midair out over Iowa in

1989.65

Behind Burcham’s data sheets, the flow

charts, diagrams, and equations, there

was, if you stopped to look, a vision, a

memory of the crippled transport in its

bizarre journey; behind the benevolently

Figure 20. Diagram

showing how much

the flight envelope

for the MD-11

expanded (in terms

of altitude in feet

and speed in knots)

during flight

research.

64 The account of the Whiskey Area flight is based on interviews with Burcham, Miller, and Maine.

65 Although I could list other test procedures that duplicate the circumstances of Flight 232, that might belabor the

point. To be fair, there is another viewpoint about the motivation for using only two engines for thrust control. Trindel

Maine wrote to this point in the original draft of this study: “Note: one of the major motivations for putting most of our

PCA development effort on the MD-11 into just the two wing engine configuration with the center engine pulled back

was to keep the research generic and applicable to other airplanes. Building a system that was critically dependent on the

center engine would not easily be generalized to the much more common matched pairs of wing engines only [in the

commercial transport fleet]. We didn’t want to design a system solely for the MD-11; we wanted to demonstrate a

general capability.”

29
xxxvi

shaped curves of the phugoid in reports, a

remembrance of something else, the

twisting frantic rush of the airplane at

impact, its bent metal gouging an 18-inchdeep hole along 4000 feet of Runway 22

at Sioux Gateway airport.

For the last hydraulics-off test on 28

November 1995, a third pilot, Ralph

Luczak, joined the PCA team in the center

seat of the cockpit. While Miller and

Fullerton handled the controls, Luczak

switched off the hydraulics systems—first

each one separately, next each combination of two, and finally all three systems.

And then the team sat, waiting to see what

the result would be. The elevators did not

move at all. The ailerons moved up,

outboard aileron at 12 degrees and the

inboard one less than half as much. The

rudder did not budge. It was not a catastrophe, but these floating surfaces resulted

in a nose-up pitch and caused a lower trim

airspeed, the opposite of what had been

predicted. The investigators had prepared

to deal with the reverse. Because airspeed

was then trimmed near minimum for

flaps-up flight, they briefly turned a

hydraulic pump on to increase speed.

Once this was accomplished, Luczak

again cut off all hydraulics, and after

reaching a stable speed of 212 knots, the

pilots proceeded with the test cards. They

lowered the landing gear with an emergency system not requiring hydraulic

pressure. The speed dropped another 17

knots. They flew a landing approach at

altitude, and the track and pitch controls

behaving normally.

The test was done.

Since these triumphs, PCA has taken a

different path. If the technology gets

attached to commercial airplanes, PCA

must survive FAA certification. On the

last day of the MD-11 demonstrations, an

FAA guest pilot addressed this step.

“Conceptually . . . a very good idea. This

demonstration effectively shows the

potential for practical implementation,”

wrote the FAA’s Tom Imrich, adding,

“more work is needed in order to move to

the regulatory credit stage.”66

One regulatory stage obstacle was retrofitting. PCA technology requires aircraft

with full authority digital engine controls,

a modification that is the wave of the

future. Unfortunately, two thirds of the

airplanes now in commercial airline fleets

do not yet have these advanced controls,

and these airplanes will remain operational for perhaps twenty-five years. For

legal reasons, the industry will not

mandate safety regulations on only a

fraction of the fleet. Many observers

noted this problem even as they applauded the MD-11 demonstrations—they

viewed the day as a glimpse into the faroff future. But Burcham refused to look at

PCA as a this-will-benefit-your-grandchildren technology. He believed it could

benefit members of your immediate

family within the next few years.

While he was at a PCA design review in

May of 1995, Burcham hit on the idea

that later became the basis for simpler

PCA systems. Most airplanes have an

autothrottle system to maintain a selected

speed, much like the cruise control in a

car. During a conversation about training

costs with a Delta pilot, he first sketched,

on another cocktail napkin, the concept of

using an autothrottle for the pitch PCA

function. Back at Dryden, controls

engineer John Burken later did an analysis

suggesting that the autothrottle could do

almost as well as the full PCA system in

controlling pitch.

Burcham later used this modified system

to eliminate the need for changes to the

engine control software. Most newer

airplanes have not only an autothrottle

system but also a digital thrust trim

system. At first Burcham called the new

approach “simplified PCA,” but Ken

Szalai soon re-christened it “PCA Lite.”

66 Tom Imrich, unpublished NASA Dryden pilot test cards, 30 November 1995.

30
xxxvii

To operate in PCA Lite, Burcham decided

to run the pitch control through the

autothrottle and use the engine thrust trim

system, which despite a plus or minus

five percent limit,67 had enough range

laterally for landing.

After the MD-11 tests concluded, PCA

entered a new stage of development with

the Dryden researchers working in close

partnership with researchers at the NASA

Ames Research Center in the Silicon

Valley. Ames provided advanced simulation testbeds with dramatically realistic

effects. Led by John Bull, a NASA

veteran now working for CAELUM

Research Corporation, these researchers

developed an effective full PCA system

for the Boeing 747. They also ran tests

with great success demonstrating PCA on

simulations for generic commercial

airliner models. When Burcham requested

sim tests for PCA Lite, Bull and his

colleagues produced effective demonstrations. Tests confirmed they could expand

the number of airplanes available for

PCA, make this new version cheaper, and

fly reasonably well with PCA Lite.68

The older airplanes that did not have

digital engine controls required a different

solution. The next innovation addressed

airplanes having autothrottle but no

engine thrust trim system. Burcham

called it “PCA Ultralite,” an arrangement

requiring the pilot to manually operate the

throttles for lateral control—a possible

but difficult workload. PCA Ultralite by

itself did not work well, but the DrydenAmes team added an improvement, using

the flight director needle in the cockpit.

This step allowed the pilot to get effective

lateral control by moving the throttles

based on cues on the flight director

needle. Pilot evaluations at Ames in 1998

confirmed the results.

After successful Lite and Ultralite demonstrations, much remained to sift. The

requirements of FAA certification are as

complex and multilevel as the product it

safeguards. Certification was not one big

test. Rather, it was a proliferation of

smaller tests, crucial in every case. Since

the MD-11 days, the researchers have

experimented on the C-17, a military jet

transport that in many ways is characteristic of the next generation of large

airplane. They have flown extensive

Boeing 747 and Boeing 757 simulations.

Experiments have included flying TOC

tests on the U.S. Navy F-18. This new

stage of experiment has involved flying

many airplanes, dealt with a great variety

of damages and looked at employing PCA

as one element in post-catastrophe

reconfiguration. The engineers have

shown how a commercial airliner without

flight controls and without an operating

engine on one wing can engage PCA by

using fuel transfer to offset the center of

gravity toward the operating engine. John

Bull and his colleagues at NASA Ames

have fashioned a brilliant sim demonstration: the Boeing 747 has its hydraulics

fail at 35,000 feet, rolls until it is upside

down, and then the PCA mode is engaged. The airplane rights itself, levels its

wings, and comes in for a safe landing

nearly identical to a normal auto landing.69

If PCA prevails, however, it will not be

because of brilliant technology. As many

observers will tell you, the decision will

be political, and in a multibillion-dollar

industry and regulatory web, “political”

means financial.

67 That is, plus or minus five percent of the full range of engine operation.

68 See Frank W. Burcham, Using Engine Thrust for Emergency Flight Control: MD-11 and B-747 Results (Edwards, CA:

NASA TM -1998-206552, May 1998).

69 The sources for this section are mostly interviews with Maine and Burcham. Also see John Bull, Piloted Simulation Tests

of Propulsion Control as a Backup to Loss of Primary Flight Controls for a Mid-Size Jet Transport (Moffett Field, CA:

NASA TM 110374, 1995).

31
xxxviii

PCA is inexpensive technology. Burcham

and his colleagues have transformed a

catastrophic scenario without adding any

hardware to most transport airplanes. The

expenses are software modification and

training. But how much are aviation

companies willing to spend on a backup

system for a remote possibility of catastrophe? After the Flight 232 crash landing, the airplane manufacturer corrected

the system, but it is a partial-control fix

and reports persist that pilots who train to

use it encounter difficulties. The industry

attitude concerning the Sioux City crash

has been: “This will never happen again.”

The real question is, how remote is

remote?

Ultimately, how will the FAA review this

new technology? If PCA is judged against

the yardstick of normal control-surface

landings, it has shortcomings. The engineers have not yet resolved, for instance,

some limits on its lateral response and

difficulties landing in heavy turbulence.

But do you judge a safety backup by the

standards of a normal landing? Would you

judge a parachute’s descent by the industry-standard for an airframe’s landing? At

the end of the MD-11 project, Jeff Kahler

performed some risk calculations based

on the sum of the guest pilot approaches,

go-rounds, and simulation studies. He

calculated that 96 landings would have

been rated safe landings and four would

not, although these were “survivable.”

Kahler figured that in 100 attempts, PCA

provided 100 survivable landings.70

If you should ever find yourself a passenger on a commercial airliner that has lost

all hydraulics or flight controls, how

satisfied could you be with your 50/50

chance of a crash landing when a technology was available which offered 100 out

of 100 survivable landings? Although no

one wants to anticipate a major catastrophe, the commercial aviation world may

Figure 21. Gordon

Fullerton in the

Boeing 747 simulator at NASA’s Ames

Research Center.

(NASA photo

AC97-0295-15 by

Tom Trower).

70 Jeff Kahler, interview by telephone with author, 24 June 1998.

32
xxxix

Figure 22. Bill

Burcham’s Ultralite

napkin showing the

basic concept for

PCA Ultralite;

CLAWS stands for

control laws; A/T

means autothrottle;

the symbols along

the horizontal line

at the bottom of the

diagram stand for

flightpath angle,

flightpath angle

rate, and airspeed.

(NASA photo

EC98-44690-1 by

Brent Wood).

have its eyes on this one. A major disaster

may cost nowadays, it has been estimated,

nearly a billion dollars. But if there should

ever occur another hydraulics-loss

crash—there have been more than a half

dozen in the last generation—given the

stacks of reports on PCA, the wide

industry awareness, the damage-suit

lawyers would stand up before juries and

have a field day.

In the end, economy may decide. But it

may or may not be lawsuit economy.

Dana Purifoy looks ahead to a PCA

system that is “not a stand alone, but an

integrated flight control.”71 Some observers see PCA as a backup to replace one of

the backup hydraulic systems. Because

PCA is only software, the savings in

airplane weight would result in significant

fuel savings. One study shows cost

savings of 140 million dollars for a fleet

of 300 airplanes.

Many of the decisions about PCA will be

made by players in an industry that rarely

shows its hand or explains decision

factors. But the NASA team is optimistic

this safety backup technology will prevail.

Burcham, continuing to refine PCA,

merely shrugs, “I just hope it never has to

be used.” Other researchers look back on

their roles in PCA’s development and at

the same time view it from a human angle

and voice a great deal of pride. “I know

someday I will see this implemented,”

says Joe Conley, “and it’s going to save

the lives of many people.”72

71 Purifoy interview.

72 Conley interview.

33
34xl
xli

Appendices

35
xlii

Appendix A

Aircraft Accident Report

United Airlines Flight 232

Sioux Gateway Airport

Sioux City, Iowa

July 19, 1989

“About 1 hour and 7 minutes after takeoff [in a DC-10]. . . the flightcrew heard a loud bang or an explosion,

followed by vibration and a shuddering of the airframe. After checking the engine instruments, the flightcrew

determined that the No. 2 aft (tail-mounted) engine had failed.” The crew soon determined further that there

was no hydraulic pressure to operate the normal flight controls.

After the flight attendants had informed the passengers of the problem and plans to attempt a landing at Sioux

Gateway Airport, “a flight attendant advised the captain that a UAL [United Airlines] DC-10 training check

airman [pilot who checks the proficiency of other airline pilots], who was off duty and seated in a first class

passenger seat, had volunteered his assistance. The captain immediately invited the airman to the cockpit. . . .”

The check pilot ascertained that the flight control surfaces were not moving, so the captain directed him “to

take control of the throttles to free” him and the first officer “to manipulate the flight controls.”

The check airman attempted to use engine power to control pitch and roll. He said that the airplane had a

continuous tendency to turn right, making it difficult to maintain a stable pitch attitude. He also advised that

the No. 1 and No. 3 engine1 thrust levers could not be used symmetrically, so he used two hands to manipulate the two throttles.”

At this time (about 26 minutes after the explosion), the second officer inspected the tail area and reported

“damage to the right and left horizontal stabilizers.”

Fuel was jettisoned to the level of the automatic system cutoff, leaving 33,500 pounds. About 11 minutes

before landing, the landing gear was extended by means of the alternate gear extension procedure.”

The flight crew reported that it sighted the airport “about 9 miles out. ATC [air traffic control] had intended

for flight 232 to attempt to land on runway 31, which was 8,999 feet long. However, ATC advised that the

airplane was on approach to runway 22, which was closed. . . . “ It said “that the length of this runway was

6,600 feet. Given the airplane’s position and the difficulty in making left turns, the captain elected to continue

the approach to runway 22 rather than to attempt maneuvering to runway 31.” The check pilot stated his

belief that “the airplane was lined up and on a normal glidepath to the field. The flaps and slats remained

retracted.”

“During the final approach, the captain recalled getting a high sink rate alarm from the ground proximity

warning system (GPWS). In the last 20 seconds before touchdown, the airspeed averaged 215” knots as

indicated by the aircraft’s instruments, “and the sink rate was 1,620 feet per minute. Smooth oscillations in

pitch and roll continued until just before touchdown when the right wing dropped rapidly.” At “about 100 feet

above the ground [according to the captain’s statement] the nose of the airplane began to pitch downward. He

also felt the right wing drop down about the same time. Both the captain and the first officer called for

reduced power on short final approach.”

1 These engines were on the left and right wings, respectively.

36
xliii

The check pilot “said that based on experience with no flap/no slat approaches[,] he knew that power would

have to be used to control the airplane’s descent. He used the first officer’s airspeed indicator and visual cues

to determine the flightpath and the need for power changes. He thought that the airplane was fairly well

aligned with the runway during the latter stages of the approach and that they would reach the runway.”

However, “soon thereafter, he observed that the airplane was positioned to the left of the desired landing area

and descending at a high rate. He also observed that the right wing began to drop.” He manipulated “the No.

1 and No. 3 engine throttles until the airplane contacted the ground. He said that no steady application of

power was used on the approach and that the power was constantly changing. He believed that he added

power just before contacting the ground.”

“The airplane touched down on the threshold slightly to the left of the centerline on runway 22 at” some 44

minutes after the explosion. “The first ground contact was made by the right wing tip[,] followed by the right

main landing gear. The airplane skidded to the right of the runway and rolled to an inverted position.”

Witnesses said the airplane ignited and did a cartwheel, “coming to rest after crossing runway 17/35.

Firefighting and rescue operations began immediately, but the airplane was destroyed by impact and fire.”

“Injuries to Persons

* One passenger died 31 days after the accident as a result of injuries he had received in the accident. In

accordance with legal precedent, “his injuries were classified ‘serious.’”

Source: Quoted and paraphrased from National Transportation Safety Board Aircraft Accident Report, United

Airlines Flight 232 (Washington, DC: PB90-910406 NTSB/AAR-90/06, 1 Nov. 1990), pp. 1-5.

Crew

1

6

4

0

11

Passengers

110

41*

121

13

285

Other

0

0

0

0

0

Total

111

47

125

13

296

Injuries

Fatal

Serious

Minor

None

Total

37
xliv

Appendix B

Flight Simulator Studies

As a result of the accident, the Safety Board directed a simulator reenactment of the events leading to the

crash. The purpose of this effort was to replicate the accident airplane dynamics to determine if DC-10

flightcrews could be taught to control the airplane and land safely with no hydraulic power available to

actuate the flight controls. The simulator exercise was based only on the situation that existed in the Sioux

City accident—the failure of the No. 2 (center) engine and the loss of fluid for all three hydraulic systems.

The DC-10 simulator used in the study was programmed with the aerodynamic characteristics of the accident

airplane that were validated by comparison with the actual flight recorder data. The DC-10 rated pilots,

consisting of line captains, training clerk airmen, and production test pilots[,] were then asked to fly the

accident airplane profile. Their comments, observations, and performance were recorded and analyzed. The

only means of control for the flight crew was from the operating wing engines. The application of asymmetric power to the wing engines changed the roll attitude, hence the heading. Increasing and decreasing power

had a limited effect on the pitch attitude. The airplane tended to oscillate about the center of gravity (CG) in

the pitch axis. It was not possible to control the pitch oscillations with any measure of precision. Moreover,

because airspeed is primarily determined by pitch trim configuration, there was no direct control of airspeed.

Consequently, landing at a predetermined point and airspeed on a runway was a highly random event.

Overall, the results of this study showed that such a maneuver involved many unknown variables and was not

trainable, and the degree of controllability during the approach and landing rendered a simulator training

exercise virtually impossible. However, the results of these simulator studies did provide some advice that

may be helpful to flight crews in the extremely unlikely event that they are faced with a similar situation. This

information has been presented to the industry by the Douglas Aircraft Company in the form of an “All DC10 Operators Letter.” In addition to discussing flight control with total hydraulic failure, the letter describes a

hydraulic system enhancement mandated by an FAA Airworthiness Directive. . . .

Source: Quoted from National Transportation Safety Board Aircraft Accident Report, United Airlines Flight

232 (Washington, DC: PB90-910406 NTSB/AAR-90/06, 1 Nov. 1990), pp. 72-73.

38
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Appendix C

National Transportation Safety Board Recommendation

Encourage research and development of backup flight control systems for newly certified wide-body airplanes

that utilize an alternative source of motive power separate from that source used for the conventional control

system. (Class II, Priority Action) (A-10-168)

Source: Quoted from National Transportation Safety Board Aircraft Accident Report, United Airlines Flight

232 (Washington, DC: PB90-910406 NTSB/AAR-90/06, 1 Nov. 1990), p. 102.

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Appendix D

Guest Pilot Comments on

the Propulsion Controlled Aircraft System

Flown on the F-15 Highly Integrated

Digital Electronic Control Aircraft

A group of propulsion-controlled aircraft [PCA] guest pilots, who flew the F-15 equipped with PCA, were all

test pilots; their comments and recommendations for added features are presented here. . . . [Note: Some of

the guest pilots worked at NASA Dryden, and their comments were so brief and non-specific that they were

not included in the technical report from which these comments are taken. The comments included here go

into greater detail and are representative of the tenor of the remaining comments.]

EXCERPTS FROM GUEST PILOT C

The evaluation was flown in clear weather with more than 30 n. mi. [nautical miles] visibility. Winds were at

magnetic heading of 240° at a speed of 18 knots gusting to 26 knots. All approaches were flown to runway 22.

Control Augmentation System-Off Control

With the CAS [control augmentation system] off, the aircraft responded sluggishly in all axes. In addition,

fine-tracking tasks were difficult to complete, and the completed task [was]only marginally adequate.

Throttles-Only Manual Control

Throttles-only manual flight was extremely difficult, if not impossible, without a large amount of training.

The major problem was controlling the phugoid in pitch. The anticipation required to achieve such control

was monumental. Using differential thrust to control roll was marginal at best, and it was fairly easy to use the

wrong throttle when trying to control bank. The throttles-only manual flight condition was unsatisfactory and

would not be recommended for use in any ejection-seat-equipped aircraft.

Propulsion-Controlled Aircraft System Control

The airplane responded adequately to all inputs commanded by the pilot. Pitch and roll response were very

sluggish, yet always consistent and, therefore, predictable. The phugoid was suppressed by the system and

was not noticeable except when making large changes in pitch. The dutch roll was well-controlled by the

system. Generally, the system provided excellent flightpath stability and good control of the aircraft without

being overly sensitive to gusts.

Unusual Attitude Recovery

The airplane was flown with the CAS off, at 250 KCAS [calibrated airspeed expressed in knots] and at an

altitude of 10,000 ft m.s.l. [above mean sea level], to a –10° flightpath angle and then banked to approximately 75°. When this attitude was achieved, the flight controls were released, the inlets were selected to the

emergency position, and the PCA system was engaged. Only the PCA system was used to recover the aircraft.

Initially, a level flight attitude was selected at the thumbwheels. The aircraft pitched up and basically entered

the phugoid mode, slowing down in the climb. Right bank was selected with the thumbwheels to aid the

nosedrop and minimize the airspeed bleed off. While on the downswing of the phugoid motion, the gear and

flaps were extended. This action was accomplished on the descending portion of the phugoid to minimize the

effects of the increased pitching moment caused by flap extension. Unusual attitude recovery was easy and

40
xlvii

effective using the PCA system controls, and at no time was the pilot concerned about the aircraft position

because of PCA system performance.

Instrument Descent

Two instrument descents were flown during the flight evaluation. The pitch response was solid. At this point,

flightpath and speed stability were also good. The aircraft performance during these maneuvers was similar to

those observed in basic autopilots capable of speed and attitude hold.

Final Approach

Four approaches were attempted with the full PCA system. A visual approach to a safe position from which to

land was consistently achieved using the PCA system.

Go-Around

A go-around using the PCA system was completed during the PCA system approach to 100 ft AGL [above

ground level]. The PCA system allowed a timely and safe go-around without requiring undue pilot effort or

skill.

EXCERPTS FROM GUEST PILOT D

The weather at engine start included a scattered-cloud layer at 6000 ft, winds at a heading of 230[°] and a

speed of 14 knots, and light turbulence from the surface to an altitude of 8000 ft. Turning all three CAS axes

off and selecting the emergency position for the pitch and the roll ratios resulted in the expected: very sloppy

handling characteristics. The airplane was difficult to trim in the roll and pitch axes. The pitch axis required a

larger than expected amount of noseup trim to stabilize at 150 KCAS. Once trimmed, the pilot released the

control stick and attempted to maintain level flight and capture a heading by manually adjusting the throttles.

Even though the air was very smooth at these 8000- to 9000-ft m.s.l. test conditions, aircraft control was very

poor. The velocity vector varied ± 4°, and the pilot overshot the intended heading by 7°. Rather than continuing to try to fine-tune this manual control, the pilot engaged the PCA system. The immediate increase in

airplane controllability was very dramatic. Small flightpath angle changes to a maximum of 2° were made

very accurately, and the first heading capture attempt was only overshot by 2°. The second PCA approach was

to 100 ft AGL at 150 KCAS and an 11° angle of attack and included a PCA system-controlled go-around.

During the approach, the pilot could hear the engines winding up and down, but the ride quality was quite

smooth. On this approach, the pilot initially biased the airplane upwind of the runway to compensate for the

crosswind. The pilot overcompensated and had to perform a sidestep to the left. That sidestep maneuver was

easy to perform. The engine speed was matched for this approach, and the roll command no longer had to be

biased one way or another.

Even though the overall turbulence seemed very similar to the previous approach, two or three upsets occurred that seemed larger than the previous approach and actually displaced the flightpath laterally. These

upsets emphasized the observation that the pilot workload was significantly higher in the roll axis than in the

pitch axis. From a –2° flightpath, pilot D used the PCA system to command a 10° flightpath angle go-around

at 100 ft AGL. The minimum altitude during this go-around was 60 ft AGL. The airplane quickly started

climbing, and the pilot had to aggressively command level flight to keep from climbing into conflicting traffic

overhead. At the end of the maneuver, the pilot was level at an altitude of 2800 ft (500 ft AGL). All in all, the

approach was very comfortable. Pilot D had good control over the aim point and had reasonably good control

over the heading of the flightpath. The third PCA system approach was flown to 50 ft AGL at 140 KCAS, then

uncoupled with the PCA engage/uncouple button and then hand-flown through a CAS-off PARRE [pitch and

roll ratios emergency] (the button is located on the right throttle) touch-and-go landing. The winds were at a

41
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heading of 230° at a speed of 19 knots gusting to 24 knots. The pilot’s overwhelming conclusion from this

approach was that the PCA system easily has sufficient authority and controllability for straight-in approaches

and for navigational maneuvers (provided the gear and flaps are down). The presence of the velocity vector

on the HUD [head-up display] was also a tremendous aid. During the approach, the pilot got low and dragged

in. As if that wasn’t enough, the pilot also got a large upset from turbulence at approximately 250 ft AGL. At

that time, the pilot made a large correction to get back on the desired flightpath. That correction bottomed out

at 160 ft AGL and then peaked at 230 ft AGL. At that point, the pilot reestablished a 2.5° glideslope and

continued with the approach. Despite this large and very late correction, the only penalty suffered was the

intended touchdown point shifted from 500 ft down the runway to 2000 ft down the runway. Of all the

maneuvers performed during the flight, that last-minute correction impressed the pilot more than anything

else. Pilot D was very pleased with the robustness and the ability of the PCA system to handle that large of a

correction in such a short time. The final approach was to 200 ft AGL at 140 KCAS using throttles-only

manual control. The workload during the manual approach was extremely high. The pilot had worked up a

sweat on the last [manual] approach. Approaching the runway, pilot D got behind on the pitch corrections, and

the flightpath angle ballooned to 6°. The subsequent pitchdown correction dropped to –7°. The pilot still did

not have this large pitch change under control using the throttles alone, so as the flightpath angle started

passing up through level flight, the pilot took over manually at 200 ft AGL. This manual approach was not

landable.

Summary

From the ground training and the demonstration profile to the PCA control law implementation, this PCA

system demonstration was very well-done. More than simply a proof-of-concept demonstrator, this flight

exhibited capabilities that would enhance the survivability of aircraft. As long as aircraft have failure modes

where the ability to fly the airplane with the control stick or yoke may be lost, this pilot would like to have the

backup capability demonstrated by the PCA system.

EXCERPTS FROM GUEST PILOT E

This flight was an evaluation flight of the F-15 PCA system. The weather was good, winds were light, and

little or no turbulence existed. After takeoff and a climb to an altitude of 7500 ft m.s.l., a short pilot evaluation

was flown with the airplane in the landing configuration, with inlets in the emergency position, and with the

CAS off. Pitch and roll ratios were also in the emergency position. Trim speed was 150 KCAS. This evaluation “warmed up” the pilot for throttles-only flying by allowing exposure to a degraded landing configuration.

In addition, the evaluation was useful in demonstrating the somewhat sluggish and imprecise basic handling

of the unaugmented F-15 airplane.

Throttles-Only Manual Control

Before approaches with the PCA system engaged, an up-and-away evaluation was flown with manual throttle

control. Up-and-away manual control of heading and changes in vertical flightpath were achieved with a high

degree of pilot workload. Many rapid, large, symmetric and asymmetric throttle movements were necessary,

few of which seemed intuitive. A satisfactory, yet imprecise, job of up-and-away control was accomplished

providing that corrections were made in a single axis. A large effort was required to damp the phugoid motion.

In addition, small precise throttle movements were hindered by the very large amounts of throttle friction. A

throttles-only manual approach was flown but aborted at less than 1000 ft AGL when pitch control was lost

during an attempt to make a lineup correction to the runway.

Coupled Approaches

Engaging the PCA system and flying with it for several minutes provides a remarkable contrast to using

42
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throttles-only manual control. Steep bank angles (25°) can be flown with full confidence, and precise (±1°)

heading and flightpath angle changes can be performed. Pilot[s’] confidence in their ability to conduct an

approach increases greatly. The tendency toward a very flat glideslope well before the threshold was finally

corrected on the third approach. The correction required aggressively, yet smoothly, driving the velocity

vector in pitch by overdriving the command box. Then, some of the commanded input was taken out when the

velocity vector neared the desired position. Laterally, a series of nearly constant small corrections was required to maintain heading.

Coupled Waveoff

On the second approach to 100 ft AGL, a go-around was initiated using only the PCA pitch thumbwheel. By

rolling the command box to an approximately 7° noseup pitch attitude, the control system added power and

flew the aircraft away with the roundout before the climb occurred at approximately 70 ft. This maneuver was

straight-forward and demonstrated another impressive system capability.

Summary

Overall, the PCA system on the F-15 airplane is a breakthrough technology that is strongly recommended for

incorporation in future or current aircraft. The system gives the pilot the ability to control and safely land an

aircraft that otherwise would crash or be abandoned before landing.

EXCERPTS FROM GUEST PILOT G

The flight was flown in the morning, but a significant crosswind and light turbulence existed. After takeoff,

pilot G flew the basic airplane CAS[control augmentation system]-off card. As expected, the airplane had

poor stability, had very light damping, rolled off quickly, was hard to trim, and was sluggish because of high

stick forces. When the PCA system was turned on, the pilot’s comment was “PCA flies the airplane really

well. The thumbwheel concept is good, and the gains are just right.” On the first approach, pilot G commented that “the airplane was real stable. I was surprised at how well the PCA held glideslope. The roll

response was really good.” On the PCA system go-around, the airplane was at a –3° glideslope at 100 ft AGL

[above ground level], but the pilot put in a big noseup command. The comment was “I was confident of the

go-around, which bottomed out 60 ft above the ground.” On the next approach to 50 ft AGL, the pilot had a

very nice approach going and said, “I think you could get the airplane on the ground from this approach in

spite of the crosswind.” The pilot then did the simulated hydraulic failure upset at an altitude of 10,000 ft,

with a 90° bank and 20° dive, and engaged the PCA system. The system rolled out aggressively, pulled

approximately 3 g [equivalent of the force of gravity] in the pull-out, and recovered nicely to level flight. The

pilot accidentally bumped the stick, which disengaged the system. This action prevented a full PCA system

descent and approach, but the pilot had no doubts that the test could have been completed. Then pilot G tried

a throttles-only manual approach, and, like all the guest pilots, had no success at all. The pilot did manage to

get the runway in sight but had to use the stick occasionally to maintain control.

EXCERPTS FROM GUEST PILOT H

The PCA system flown in the HIDEC F-15 airplane was evaluated as a highly effective backup recovery

system for aircraft that totally lose conventional flight controls. The system was simple and intuitive to use

and would require only minimal training for pilots to learn to use effectively. Of course, landing using the

PCA system would require higher workloads than normal, but this pilot believes landings could be done

safely. The fact that the system provides a simple, straight-forward, go-around capability that allows multiple

approaches further supports its safe landing capability. The dutch-roll suppression characteristics of the

system were extremely impressive to the pilot and would allow landings to be done even in nonideal wind

conditions. The pilot thought the PCA system exhibited great promise and, if incorporated into future trans43
l

port aircraft, could further improve the safety of the passenger airlines.

Control Augmentation System-Off Control

Shortly after takeoff, the aircraft was placed in the powered-approach configuration while flying straight and

level at an altitude of 6200 ft mean sea level (m.s.l.). Pilot workload in the CAS-off mode was high, and

control precision was marginal. The F-15 airplane felt sluggish in pitch and roll and was difficult to trim. The

airplane felt like a “heavier” aircraft because of slow response [pilots’s] to inputs and heavy stick forces. The

pilot had to shape or lead inputs to capture desired bank or pitch angles. Rudder doublets excited a moderately

damped dutch roll.

Manual Throttles-Only Control

Overall controllability was adequate with throttle manipulation. Bank-angle control was intuitive and fairly

easy to accomplish. Collective throttle movement provided marginally adequate pitch-angle control in the F15 airplane. Controlling one axis at a time was not too difficult, but maintaining simultaneous control of pitch

and roll required all of the pilot’s attention. Overall, throttles-only manual control would probably allow the

pilot to return to friendly territory, but pilot fatigue and task saturation could occur. The PCA system control

and approach tests are described next.

Control

The PCA system provided satisfactory control of pitch and roll axes. Bank-angle capture was generally good

with an approximately 2° oscillation about the desired bank angle. This oscillation was likely caused by

turbulence or gust response because dutch roll appeared to be well-damped by the PCA system. Flightpath

angle captures were successful using the pitch thumbwheel to position the HUD flightpath command box.

Overall, the pilot was impressed with the capability of the PCA system and the reduction in pilot workload it

afforded. A pilot could easily accomplish several other tasks while flying the aircraft in this mode.

Approach to 200 ft Above Ground Level

Pitch control was outstanding, which allowed the pilot to work almost exclusively in the roll axis. Pilot

workload in roll was high; however, the workload could have been significantly reduced if a “heading hold”

feature was incorporated. Overall pilot confidence in the PCA system during this first approach was high.

Recovery from Unusual Attitude and Descent to Approach to 20 ft Above Ground Level

This point was entered at 260 knots calibrated airspeed (KCAS) and an altitude of 10,200 ft m.s.l. [feet above

mean sea level]. The gear and flaps were up, and the inlets were in the automatic scheduling mode. The CAS

was off, and pitch and roll ratios were in the emergency position. The aircraft was then maneuvered to 90° left

wing down and 10° nosedown. Next, the pilot positioned the inlets to the emergency position to simulate

hydraulic failure and engaged the PCA system. The nose continued to drop until the wings leveled approximately 5 sec later. Maximum airspeed during the pullout was 360 KCAS. After two phugoid cycles, the

oscillatory motion was damped by the PCA system. In addition, the aircraft stabilized at 150 KCAS. A

straight-in approach was flown to runway 22 in winds at a magnetic heading of 280° and a speed of 10 knots

in light turbulence. Aggressive roll thumb-wheel action resulted in good lineup control. One item of concern

was a slight pitchdown that occurred as the airplane passed 30 ft AGL. This pitchdown appeared to be similar

to the ground effect-induced pitchdown encountered on the initial PCA system landings conducted by NASA

pilots. Overall, the ability of the PCA system to recover the aircraft from an unusual attitude at 260 KCAS and

then provide satisfactory approach control at a trim airspeed of 150 KCAS was impressive.

44
li

Manual Throttles-Only Approach to 200 ft Above Ground Level

This straight-in approach was flown to runway 22 in winds at a magnetic heading of 280° and a speed of 8

knots in light turbulence. The F-15 manual mode (throttles only, no augmentation) was unacceptable for

flying a safe or repeatable approach to landing.

Conclusions

Overall, the PCA concept demonstrates good potential for use as a backup flight control system for tactical

naval aircraft. The system provides adequate control authority for the F-15A airplane and enables repeatable,

safe approaches without the use of conventional mechanical flight controls. The pilot was impressed with the

ability of the system to precisely control bank and flightpath angles. Pilot workload throughout the PCAcoupled approaches was low relative to the throttles-only manual approach. This low workload was convincing testimony to the value of the PCA system. An aircraft employing the PCA system as the sole backup flight

control system would be able to save considerable weight by eliminating typical hydromechanical backups.

Source: Quoted with minor editing in brackets from Frank W. Burcham, Jr., Trindel A. Maine, C. Gordon

Fullerton, and Lannie Dean Webb, Development and Flight Evaluation of an Emergency Digital Flight

Control System Using Only Engine Thrust on an F-15 Airplane (Edwards, CA: NASA Technical Paper 3627,

1996), pp. 93-97.

45
lii

Appendix E

PCA System Landing

in an MD-11 Aircraft

29 August 1995

The MD-11 was flown to Edwards AFB, where a 15,000-ft long, 300-ft wide runway was used for initial PCA

landing attempts. Pilot A flew three PCA low approaches to gradually lower altitude PCA system go-arounds.

Continuous light turbulence and occasional upsets from thermals occurred; however, PCA performance was

judged adequate to proceed to PCA landings. On the first intended landing, initial lineup and flightpath

control were good. Based on simulation experience, the pilot selected a flightpath of –1° at 140 ft AGL [above

ground level]. The flightpath overshot to approximately –0.5° and then began to decrease back through the –

1° command. At 30 ft AGL, the sink rate was increasing to 8 ft/sec, so the safety pilot, as briefed, made a

small nose-up elevator input, then allowed the airplane to touch down under PCA system control. The touchdown was 25 ft left of the runway centerline, 5000 ft from the threshold at a sink rate of 4.5 ft/sec. The MD11 was stopped using reverse thrust and brakes but no spoilers or nosewheel steering.

The second landing was accomplished using a slightly different flightpath control technique. Pilot A made

small track changes to maintain runway lineup and set the flightpath command at –1.9° for the initial part of

the approach. Airspeed was 175 kn[ots] at 200 ft AGL, based on the experience with the first landing, the pilot

shallowed the flightpath to –1°, and at 100 ft to –0.5°. The airplane touched down smoothly on the centerline

at a 4 ft/sec sink rate, 3000 ft from the threshold with no inputs from the safety pilot. Note [that there was an]

upset from a thermal updraft that caused the airplane bank angle to increase to 8° at 100 ft AGL; the PCA

track mode corrected without any pilot input. The airplane was stopped using reverse thrust and light braking

but no flight control inputs. Pilot A rated the pitch control as excellent and the lateral control as adequate on

this landing.

From the two landings in light turbulence, it was observed that PCA generally controlled track and pitch to

within ±0.5° of command (disregarding the 1° bias in the track command). EPR [engine pressure ratio] values

on approach were approximately 1.15, and variations were normally approximately ±0.1; a 0.4 EPR differential thrust was used to correct for the thermal upset. Ground effect was similar to that seen in the simulator.

Later in the day, additional Flaps 28 [with flaps at an angle of roughly 28°] approaches were conducted at

Edwards AFB by pilot C. By this time, the afternoon turbulence activity had increased so much that the new

pilot using the PCA mode had difficulty adequately maintaining a stable approach. Next, three approaches

with flaps and slats retracted were conducted with a go-around at 200 ft AGL. The first approach was at

Edwards, and the last two were at Yuma. The results from all three approaches indicated that the aircraft,

using PCA system control, arrived at a suitable position to land on the runway. PCA system operation was

also evaluated en route from Edwards to Yuma using all the PCA modes. Testing during this period included

phugoid investigation, step responses, rudder trim offsets, and frequency sweeps.

The only significant problem encountered in PCA testing to this point was the sluggish and difficult-to-predict

lateral control on approaches in turbulence. Pilots found that three or four approaches were required before

adequate lineup was consistently achieved.

Source: Quoted with minor editing in brackets from Frank W. Burcham, Jr., John J. Burken, Trindel A. Maine,

and C. Gordon Fullerton, Development and Flight Test of an Emergency Flight Control System Using Only

Engine Thrust on an MD-11 Transport Airplane (Edwards, CA: NASA TP-97-206217, 1997), pp. 42-43.

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Appendix F

Summary of

Guest Pilot Comments about

Flying PCA Approaches in an

MD-11 Aircraft

29-30 November 1995

PCA pilots and observers in MD-11

Position

Chief test pilot

Vice pres., flight operations

Chief technical pilot

MD-11 chief pilot

Engineering pilot

NRS, air carrier ops

NRS, flight mgt.

Acrft. eval. group

Asst. to dir. engrng.

Deputy vice president

Vice pres., flt. ops.

Technical operations

AFFTC, 418th flight test force

AFFTC

NATC TPS

NATC TPS

Project pilot

PCA evaluation pilot

MD-11 chief pilot

PCA project pilot

MDA chief pilot

MD-11 PCA pilot

MD-11 pilot

MD-11 pilot

Director, flight test

Technical writer

Technical writer

PCA engineer

Simulation engineer

Honeywell fellow

Pvt. pilot/engineer

NASA Dryden

Name

William Wainwright

Kenneth Higgins

Tom McBroom, captain

Roy Tucker, captain

Chip Adam

Tom Imrich

George Lyddane

Carl Malone

Hiromichi Mitsuhashi, captain

Koci Sasaki, captain

Abdullah Alhabdad, captain

Ruedi Bornhauser, captain

Ed Allvin, captain

Frank Batteas, Lt Col

Bob Stoney, Lt Cdr

Steve Wright, Cdr

Gordon Fullerton

Dana Purifoy

John Miller

Ralph Luczak

Tom Melody

Walt Smith

Tim Dineen

Don Alexander

Robert Gilles

Mike Dornheim

Ed Kolano

John Bull

Don Bryant

Larry Yount

Tom Enyart

Bill Dana

Affiliation

Airbus Industrie

Boeing

American Airlines

Delta Airlines

Federal Aviation Admin.

Federal Aviation Admin.

Federal Aviation Admin.

Federal Aviation Admin.

Japan Air Lines

Japan Air Lines

Royal Flight (Saudi)

Swissair

U.S. Air Force

U.S. Air Force

U.S. Navy

U.S. Navy

NASA Dryden

NASA Dryden

McDonnell Douglas

McDonnell Douglas

McDonnell Douglas

McDonnell Douglas

McDonnell Douglas

McDonnell Douglas

Airbus Industrie

Aviation Week

Flight International

NASA Ames

NASA Ames

Honeywell

Federal Aviation Admin.

Chief engineer

47
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Following the engagement of PCA, each pilot flew a downwind and base leg to a 12-mi straight-in approach

[in the MD-11]. Each pilot then made a PCA approach to a virtual runway at 100 ft AGL [above ground level]

(the first flare was set for 230 ft AGL and the second flare to 130 ft AGL). Most used the ILS-coupled mode,

while a few used PCA FPA [flightpath angle] and TRK [track angle (magnetic heading of ground track)]

control. In the very smooth air of these tests, even the PCA approaches using the FCP [flight control panel on

cockpit glareshield] knobs were successful. At the 100-ft decision height, the pilots then pushed the TOGA

[turnoff-go-around] button on the throttles to initiate a PCA go-around. The go-around was continued with a

turn to the crosswind leg.

All pilots were very impressed with the PCA system. In general, FPA and TRK modes were preferred, although the bank angle mode and V/S [vertical speed] modes received very little evaluation. The pilots all

were impressed with the go-around capability in which less than 60 ft of altitude were typically lost. These

pilots also commented that control seemed almost normal and that, aside from the brief lateral acceleration

immediately after making a track change, they could not tell whether the engines were providing all of the

flight control. All pilots found the FCP knobs very easy and natural to use. Observers sitting in the cabin

noted no difference from a normal approach unless seated where they could hear the engine sounds changing

pitch.

The following excerpts from questionnaires summarize the demonstration pilot comments and suggestions for

additional work:

1. Conceptually, a very good idea. This demonstration effectively shows the potential for practical implementation. More work is needed in order to move to the regulatory credit stage.

2. Basic PCA track/flightpath angle is excellent for all normal tasks. Use of fully coupled ILS/MLS [microwave landing system]/FMS [flight management system], etc., is the safest concept.

3. Pilotage with manual throttle consistently induced both phugoid and dutch roll tendencies. The insertion of

PCA damped these modes out.

4. The PCA is an enhancing characteristic and will increase the level of safety of the aircraft. This technology

should be further developed.

5. I had trouble flying manual with throttles only for pitch and roll. When on auto, it smoothed out. I think this

program will be good for future backup systems, or partial control for normal systems.

6. Simulator evaluation was perfect setup to understand principles for PCA and see small throttle maneuvers.

Aircraft was easier to fly in manual mode than simulator, but got better feel for phugoid in the aircraft.

Controlled flight with autopilot more consistent than manual mode.

7. PCA manual track very controllable—smooth pitch corrections. Side force during turn initiation was

noticeable but not objectionable. Pitch and glidepath angle were easily achieved using the thumbwheel. ILS

was intercepted using this mode, and tracking, while requiring attention, was a nonevent.

8. Manual manipulation of throttles for pitch/roll control was very workload intensive. Bank control to within

5° moderately difficult. Pitch control extremely difficult. Utilization of track/bank and flightpath angle modes

was impressive. These modes took a marginally controllable aircraft (especially in pitch) and made it extremely easy to fly.

9. Manual flying—to control phugoid, needed a couple of simulator approaches for experience. But when

PCA engaged, it could be controlled perfectly. PCA flightpath angle control was smooth and better than

expected.

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10. Very useful demonstration of a system which shows good potential for use in some serious failure cases.

An obvious limitation is that the system can only work (without the center engine) about a trim speed, which

will vary with circumstances. Thus, its ability to maneuver is limited, but it works well on a well-constrained

task such as a level entry to a glideslope with a small intercept angle to the localizer.

11. Aircraft very controllable in autopilot modes (PCA). Manually, control next to impossible. Coupled, very

impressive—a safe landing should be possible.

12. Basically, takes what had been a very challenging, if not impossible, situation into what could be considered a textbook lesson with no exceptional pilot skills required.

13. Amazing! Overall, you have to see it to believe it! All involved people have done a great job.

14. I was amazed that the roll response was very quick and positive compared to the simulator. I experienced

manual throttle control[;] PCA is very helpful.

15. Pitch and roll rates experienced with the PCA system engaged were comparable with those routinely used

by the airlines. A small lateral acceleration was felt as the system commanded differential thrust. Noticeable,

but not uncomfortable, this sideways pulse was only evident with roll initiation.

Source: Quoted with minor editing in brackets from Frank W. Burcham, Jr., John J. Burken, Trindel A. Maine,

and C. Gordon Fullerton, Development and Flight Test of an Emergency Flight Control System Using Only

Engine Thrust on an MD-11 Transport Airplane (Edwards, CA: NASA TP-97-206217, 1997), pp. 74-76.

49
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Appendix G

Awards and Honors

The PCA team and project have received numerous awards and honors, including the following as of September 1997:

Discover Award for Technological Innovation, Finalist 1993

NASA Group Achievement Award, PCA project team, 19 Aug. 1993

Popular Science’s “The Best of What’s New,” the year’s 100 greatest Achievements In Science and Technology, 1993

Ray Temhoff award for best paper, Society of Experimental Test Pilots Symposium, Gordon Fullerton, 1993

Patent Award, US Patent #5,330,131 for Engines-Only Flight Control System. 19 July 1994

1994 R&D 100 awards for Propulsion Controlled Aircraft, 22 September 1994

NASA Exceptional Engineering Achievement Award 1994 (PCA)

NASA Tech Brief, 1995, Burcham, Fullerton, Gilyard, Conley, Stewart

1995 Aviation Week & Space Technology Laurel Award to Burcham and Fullerton, Jan. 1996

1995 NASA Commercial Invention of the Year Award & nominee for Government Invention of the Year

Award

1997 AIAA Guidance, Navigation, and Control Conference Best Paper, MD-11 PCA Flight test results.

1997 Flight Safety Foundation Presidential Citation

1997 Patent Award for PCA-Lite

1997 (Best paper award), Burcham, Frank W., Sitz, Joel, and Bull, John: “Propulsion Controlled Aircraft: A

Safety and Survivability Enhancement Concept,” ADPA/NSIA Symposium Paper, 23 October 1997

Source: Information provided by Mr. Burcham.

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Index

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Acronyms, 5-7

Air Force, U.S., 14

Airplane crashes, 1-2

Ames Research Center, 29, 31, 32 ill.

Aviation Week & Space Technology, 1, 22

Barber, Marvin R. (Russ), 24-25

Baron, Robert S., 24

Boeing Aerospace Corporation, 14 n, 23

Boeing 720, 7

Boeing 747, 31

Boeing 757, 31

Bull, John S., 31, 50

Burcham, Frank W., 1, 2-32, 13 ill., 18 ill., 21

ill., 27 ill., 50

Burken, John J., 6, 18, 24, 26, 28, 27 ill., 28, 30

C-5, 12

C-17, 31

Conley, Joseph L., 7, 11, 12, 27, 33, 50

Controlled Impact Demonstration (CID), 7

Control laws, 7-8

Control surfaces, 4, 15, 16, 19, 25, 26, 28, 30, 32

Crashes, 2, 12, 29-30, 32, 36-38

Deets, Dwain A., 23

Digital computers, 2, 14

Digital electronic engine controls, 14, 23, 30

Digital Electronic Flight Control System

(DEFCS), 1 ill.

Douglas Aircraft, 24, 26, 28

Dryden Flight Research Center, 1, 3, 27 ill.,

passim

Dutch roll, 4 ill.

Edwards Air Force Base, CA, 1, 3, 22, 26 ill., 27

F-4 Control Configured Vehicle (CCV), 15-16

F-15, 2 ill., 6 ill., 14, 15 ill., 16 ill., 17-18, 19 ill.,

20 ill., 21 ill., 40-45

F-18, 31

Feather, John, 24, 27 ill.

Federal Aviation Administration (FAA), 5, 7, 30,

31, 32

Fitch, Dennis, 2, 6, 11, 16, 29

Flight Control Computer (FCC), 14, 24

Flight research, 16-18, 20-22, 25-27, 28-30

Fullerton, Charles Gordon, 10-13, 13 ill., 15 ill.,

15-18, 20 ill., 20-22, 21 ill., 26, 27 ill., 28-30,

32 ill, 50

Funding, 10, 14, 24

General Electric, 24

Gilyard, Glenn B., 7-8, 21, 50

Ground effects, 19-20

Guest pilots, 22, 27-28, 40-45, 47-49

Hamilton, Len, 22

Haynes, Al, 2, 12-13, 13 ill., 16, 25, 29

Highly Integrated Digital Electronic Control

(HIDEC), 1 ill., 2 ill., 3, 6, 14, 15

Honeywell, 24, 27

Hydraulic controls, 1, 19, 25

Imrich, Tom, 30

Inlet effects, 19

Instrument Landing System (ILS), 12, 27

Japan Airlines, 12

Kahler, Jeff, 24, 26, 27, 32

King, John, 23

Langley Research Center, 23

Lauber, John, 23

Le, Jeanette H., 7-8

Luczak, Ralph, 24, 29

Maine, Trindel A., 3 n, 18 ill., 19-20, 24

McDonnell Douglas Aerospace, 14, 19, 22, 23,

24

MD-11, 22 ill., 23-30, 26 ill., 27 ill., 29 ill., 46-

49

Miller, John, 24, 26, 28, 30

National Aeronautics and Space Administration,

23; see also Ames, Dryden, Langley

National Transportation Safety Board (NTSB), 5,

23, 38-39

Neighbor, Terry, 14

Pappas, Drew, 24-25, 27

Petersen, Kevin L., iv, 7

Phugoid oscillation, 3 ill., 4

52
lix

Pratt & Whitney, 20, 24

Project managers, 24

Propulsion Controlled Aircraft (PCA) project,

1 ill., 3 n, 4-33, 33 ill., 40-45

PCA Lite, 30-31

PCA Ultralite, 31, 33 ill.

Purifoy, Dana, 4, 10, 24, 28, 33

Risk calculations, 32

Simulation, 6 ill., 7-8, 10, 14-15, 18, 24, 18-20,

24, 29, 30, 38

Sioux Gateway Airport, 2, 12, 30, 32, 36-38

Sitz, Joel R., 24, 28, 50

Skepticism about PCA, 9, 12, 18

Smith, Walt, 24

Stewart, James F., Dr., 2, 3-4, 5, 9, 11, 12, 13 ill.,

50

Szalai, Kenneth J., 9-10, 30

Throttles Only Control (TOC), 7, 11, 16, 31

Thumbwheels, 11, 15-16, 26

Urnes, James, 14, 21, 22

Vietnam, 12

Wells, Edward, 14-15, 21

Whitehead, Robert E., Dr., 23

Wolf, Thomas D., 6, 15

Yeager, Bob, 16

Yuma, AZ, 26

53
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About the Author

Tom Tucker is a writer who has a special interest in topics relating to invention. He is the author of Brainstorm: The Stories of Twenty American Kid Inventors (New York: Farrar, Straus & Giroux, 1995, revised

1998) and “Bolt of Fate: Benjamin Franklin and His Electric Kite Experiment” (due from Foreign Affairs

Books in 2000). He has published in many periodicals and also has written about baseball, including a

baseball short story featured in Sports Illustrated. He is an instructor at Isothermal Community College in

Spindale, NC. He attended Harvard College and Washington University in St. Louis, earning his B.A. and

later an M.A. on a Woodrow Wilson Fellowship at Washington University.

Monographs in Aerospace History

This is the seventeenth publication in a new series of special studies prepared under the auspices of the NASA

History Program. The Monographs in Aerospace History series is designed to provide a wide variety of

investigations relative to the history of aeronautics and space. These publications are intended to be tightly

focused in terms of subject, relatively short in length, and reproduced in inexpensive format to allow timely

and broad dissemination to researchers in aerospace history. Suggestions for additional publications in the

Monographs in Aerospace History series are welcome and should be sent to Roger D. Launius, Chief Historian, Code ZH, National Aeronautics and Space Administration, Washington, DC, 20546. Previous publications in this series are:

Launius, Roger D. and Gillette, Aaron K. Compilers. Toward a History of the Space Shuttle: An Annotated

Bibliography. (Monographs in Aerospace History, Number 1, 1992)

Launius, Roger D. and Hunley, J. D. Compilers. An Annotated Bibliography of the Apollo Program. (Monographs in Aerospace History, Number 2, 1994)

Launius, Roger D. Apollo: A Retrospective Analysis. (Monographs in Aerospace History, Number 3, 1994)

Hansen, James R. Enchanted Rendezvous: John C. Houbolt and the Genesis of the Lunar-Orbit Rendezvous

Concept. (Monographs in Aerospace History, Number 4, 1995)

Gorn, Michael H. Hugh L. Dryden’s Career in Aviation and Space. (Monographs

in Aerospace History, No. 5, 1996).

Powers, Sheryll Goecke. Women in Aeronautical Engineering at the Dryden

Flight Research Center, 1946-1995. (Monographs in Aerospace History, No. 6,

1997).

Portree, David S.F. and Trevino, Robert C. Compilers. Walking to Olympus: A

Chronology of Extravehicular Activity (EVA). (Monographs in Aerospace

History, No. 7, 1997).

Logsdon, John M. Moderator. The Legislative Origins of the National

Aeronautics and Space Act of 1958: Proceedings of an Oral History Workshop.

(Monographs in Aerospace History, No. 8, 1998).

Rumerman, Judy A. Compiler. U.S. Human Spaceflights: A Record of

Achievement, 1961-1998. (Monographs in Aerospace History, No. 9, 1998).

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Portree, David S.F. NASA’s Origins and the Dawn of the Space Age.

(Monographs in Aerospace History, No. 10, 1998).

Logsdon, John M. Together in Orbit: The Origins of International

Cooperation in the Space Station Program. (Monographs in Aerospace History,

No. 11, 1998).

Phillips, W. Hewitt. Journey in Aeronautical Research: A Career at NASA

Langley Research Center. (Monographs in Aerospace History, No. 12, 1998).

Braslow, Albert L. A History of Suction-Type Laminar-Flow Control with Emphasis on Flight Research.

(Monographs in Aerospace History, No. 13, 1999).

Logsdon, John M. Moderator. Managing the Moon Program: Lessons Learned from Project Apollo (Monographs in Aerospace History, No. 14, 1999).

Perminov, V. G. The Difficult Road to Mars: A Brief History of Mars Exploration in the Soviet Union (Monographs in Aerospace History, No. 15, 1999).

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