National Transportation Safety Board 

Washington, DC 20594 

Office of the Chairman 

April 8, 2015 

The Honorable Michael P. Huerta 

Administrator 

Federal Aviation Administration 

Washington, DC 20591 

Dear Administrator Huerta: 

Thank you for your February 5, 2015, letter to the National Transportation Safety Board 

regarding Safety Recommendations A-09-55 through -58, and A-09-60. We issued these 

recommendations to the Federal Aviation Administration on July 17, 2009, as a result of our 

investigation of the September 19, 2008, runway overrun by a Bombardier Learjet 60, operated 

by Global Exec Aviation, while departing Columbia Metropolitan Airport, Columbia, 

South Carolina. 

A-09-55 

Require Learjet to change the design of the Lea1jet 60 thrust lever system in 

future-manufactured airplanes so that the reverse lever positions in the cockpit 

match the positions of the thrust reverser mechanisms at the engines when the 

thrust reversers stow. 

A-09-56 

Once design changes are developed per Safety Recommendation A-09-55, require 

Learjet 60 operators to retrofit existing airplanes so that the reverse lever positions 

in the cockpit match the positions of the thrust reverser mechanisms at the engines 

when the thrust reversers stow. 

A-09-57 

l0150<l il 3 

Require Learjet to develop and install improved aural or visual cues on future 

manufactured Learjet 60 airplanes that would allow pilots to recognize an 

inadvertent thrust reverser stowage in a timely manner. 
2 

A-09-58 

Once improved aural or visual cues are developed per Safety Recommendation 

A-09-57, require Learjet 60 operators to install those cues on existing Learjet 60 

airplanes. 

Your current letter discusses the June 13, 2013, issuance of airworthiness 

directive (AD) 2013-13-09, which requires installing new rigid hydraulic tube assemblies to the 

main landing gear (MLG) struts, modifications to the MLG squat switch system, improved 

wheel well electrical wiring protection, and system shielding; and the April 1, 20 10, issuance of 

AD 20 I 0-1 I -II to reduce the risk of tire fai lure on Learjet 60 airplanes, including revisions to 

the crew procedures for an aborted takeoff and inadvertent stow of thrust reverser after a 

crew-commanded deployment. We have previously said that these developments are 

commendable and needed improvements, but they are not relevant to these recommendations. 

You previously told us that you had determined that an unsafe condition existed when full 

reverse thrust is commanded but full for.vard thrust is obtained after a failure, and that, as a 

result, Learjet was developing a change to the thrust reverser system on the Learjet 60 to mitigate 

this unsafe condition. You said that you planned to certify Learjet's revised design. We replied 

that these were positive steps towards satisfying Safety Recommendations A-09-55 and -56. ln 

your previous letter, you also told us that you believed that the changes being made to the thrust 

reverser actuator controls also addressed Safety Recommendations A-09-57 and -58. We did not 

agree, and we said that the need remained for the development and installation of aural or visual 

cues when the thrust reversers had not deployed as commanded. 

In your current letter, this situation is now reversed. Learjet is developing an aural 

warning as recommended in Safety Recommendation A-09-57, but work on the design change to 

make the positions of the thrust reverser levers match the positions of the thrust reversers is on 

hold pending development of the proposed aural warning. You state that you believe the aural 

warnin g may be a more cost-effective and readily implemented alternative to the actions 

specified in Safety Recommendations A-09-55 and -56. 

We continue to believe that all four recommended actions are necessary and that none of 

the actions for any one or pair of these recommendations is an acceptable alternative for the 

others. Because you have placed the planned activity on hold, Safety Recommendations A-09-55 

and -56 are classified "Open- Unacceptable Response" pending completion of the 

recommended actions. Because Learjet is now designing a system to provide an aural warning, 

Safety Recommendations A-09-57 and -58 are classified "Open- Acceptable Response" pending 

completion of this system, your review and certification of the system, and your requiring that it 

be incorporated into newly manufactured and in-service Learjet 60 airplanes. 

A-09-60 

Evaluate the design of the thrust reverser controls and indications in 

Raytheon Hawker I 000 business jets for potential thrust reverser failure modes 
3 

that are similar to those identified 111 Learjet 60 airplanes and implement 

necessary changes. 

We note that you continue to evaluate the effectiveness of the design change that 

Textron Aviation-Beechcraft (formerly Hawker Beechcraft Company) developed to ensure that 

the engine remains at idle following a failure causing an uncommanded stow of the 

thrust reverser. We further note (1) that Textron Aviation is integrating Beech craft and Cessna 

into a single company, (2) that the company is in the process of completing certification tasks 

associated with the design change, and (3) that you asked Textron Aviation-Beechcraft to provide 

a schedule update for their next tasks. Pending completion of the recommended action, Safety 

Recommendation A-09-60 remains classified "Open-Acceptable Response." 

Please submit updates electronically at correspondence@.ntsb.gov regarding your actions to 

address these recommendations. Please do not submit both an electronic copy and a hard copy of the 

same response. 

cc: Ms. Barbara McCann, Director 

Office of Safety, Energy, and 

Environment 

Office of the Under Secretary for Policy 

Sincerely, 

&·ristophcr A. Hart · '/. Chnirmnn ..... • A..'\?:tJH'rl ;rY crt·C:tc.r.:c il.itW~t ~·dl' 

N' 1-lon: ~" .tr Fuo·..., 
National Transportation Safety Board 

Washington, D.C. 20594 

The Honorable J. Randolph Babbitt 

Administrator 

Federal Aviation Administration 

Washington, D.C. 20591 

Safety Recommendation 

Date: July 17, 2009 

In reply refer to: A-09-55 through -60 

On September 19, 2008; about 2353 eastern daylight time, a Bombardier Learjet 60 

(Learjet 60), N999LJ, operated by Global Exec Aviation, overran runway ll while departing 

Columbia Metropolitan Airport, Columbia, South Carolina. ' The pilot, copilot, and two of the 

four passengers were killed; the two other passengers were seriously injured. The aircra ft was 

destroyed by postcrash fire. Visual meteorological conditions prevailed, and an instrument flight 

rules flight plan was filed for the 14 Code of Federal Regulations (CFR) Part 135 nonscheduled 

domestic passenger flight to Van Nuys, California. 

According to witness interviews and the cockpit voice recorder (CVR) transcript, the 

beginning of the takeoff roll appeared normal. However, sparks were observed as the airpl ane 

traveled along the runway. The airplane then continued beyond the runway and through the 

approximately 1,000-foot runway safety area and, beyond that, struck airport lighting, navigation 

facilities, a perimeter fence, and concrete marker posts. The airplane then crossed a roadway and 

came to rest when it struck an embankment across the road from the airport. 

Postacc ident examination of markings and tire debris indicated that the ri ght outboard tire 

fai led fi rst because of underinflation, followed by failures of the other tires.

2 Examination of the 

engines revealed evidence consistent with high thrust in both engines and indicated that the 

th rust reversers were stowed when the airplane hit the embankment. 

The National Transportation Safety Board's (NTSB) investigation of this accident is 

ongoing. Hovvever, on the basis of preliminary findings, the NTSB is concerned abo ut safety 

1 More information about this accident, DCA08MA098, is available on the National Transportation Safety 

Board 's website at <http://www.ntsb.gov/ntsb/query.asp>. 

2 Duri ng the investigation, the NTSB found evidence that the accident airplane's tires were underinflated. 

Review of tire fragments revealed that there was extensive heat damage within the tire construction; excessive 

weight (overflexu re) of the rubber c reated the heat. No evidence of excessive brake heating was found. The tires are 

being separately addressed. 

806JA 
2 

issues involving inadvertent stowage3 of the thrust reversers. In March 2009, Learjet published a 

Federal Av iation Administration (FAA)-approved temporary flight manual (TFM) change in 

procedures, which described improved methods for quickly recognizing and ha ndli ng situations 

when inadvertent stowage occurs. However, the NTSB is concerned that Learjet 60 pi lots are not 

sufficiently trained to recognize that a t~lilurc could occur during takeoff as well as landing 

phases of flight and could subsequently result in the loss of system logic control requirements for 

maintaining deployed thrust reversers during a rejected takeoff. The design of the Learjet 60 

thrust reverser system (and potentially similarly designed systems for Raytheon Hawker 1000 

business jets) is also of concern to the NTSB. Information supporting six recommendations to 

address these safety issues is discussed below. 

Design ofLearj et 60 Thrust Lever System 

Review of the CVR revealed that the first indication of tire damage occurred after the 

airplane had passed V 1

4 and that fl ight crew actions were consistent with a decision to reject the 

takeoff. 5 The Learjet 60 rejected takeoff procedure calls for the pilot to reduce thrust to idle, 

deploy the reverse levers, and then increase thrust while in reverse. A sound spectrum analysis of 

the CVR indicated that the engine power was reduced and then increased to about 80 percent of 

maximum power, consistent with the pilot following the rejected takeoff procedure. 

On most transport-category airplanes, including the Learjet 60, to deploy the thrust 

reversers, the pilot first moves the engine power levers to id le then pulls the reverse levers 

upward. The levers' upward deflections determine how much reverse thrust is created. In 

Learjet 60 airplanes, there is no mechanical or cable-actuated connection between the reverse 

levers and the engine thrust reversers. When the reverse levers are raised, an electrical signal 

commands the thrust reversers to go to a reverse thrust position. The system must meet certain 

requirements before the thrust reversers will move to a reverse thrust position; for example, the 

air/ground sensor squat switches, located on the main landing gear, must indicate that the 

airplane is on the ground (by detecting weight on wheels). The electronic engine contr()ls have 

no ability to automatically return the reverse levers ·to the idle positions and do not reduce the 

thrust if the system control logic requirements for keeping the thrust reversers deployed are no 

longer being met. In addition, the thrust reversers are designed to fai l to the stowed position to 

allow forwa rd thrust and prevent reduction of pilot control in flight. 

The wiring for the accident airplane's right squat switch was routed along the ri ght main 

landing gear strut between the right tires. Glass from the adjacent landing light and evidence of a 

broken hydraulic hose were found among the first tire fragments, and data on the CVR ind icated 

3 Although this situation is referred to as "inadvertent" stowage, it is not the result of any c rew-commanded 

action. 

4 V 1 is the takeoff decision speed or critical engine failure speed. Following a failure of the critical engine, V 1 is 

the minimum speed in the takeoff at which the pilot can continue takeoff and achieve the required height above the 

takeoff surface within the takeoff distance. V 1 is also the maximum speed in the takeoff at which the pilot must take 

the first action (for example, apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the 

accelerate-stop distance. 

5 The tires began to fai l just as the first officer said, "V 1." In addition, during the investigation, the NTSB 

learned about an FAA test pi lot of a Learjet 55 who rejected a ta keoff after multiple tires fa iled at V 1; the pilot 

reported that he made the decision because he was afraid that the engines would ingest numerous large tire pieces 

that were being thrown past the cockpit windows. 
3 

that a squat switch circuit went to the "air" mode during the accident sequence.6 These findings 

are strong indications that the squat switch wiring was probably damaged when the tires failed . 

Thus, with the loss of the on-ground signal, the system would have moved both thrust reversers 

to the stowed position (the position in which the accident airplane's thrust reversers were found). 

Accord ingly, the engines would have provided forward thrust commensurate with the angle of 

the thrust lever position commanded by the pilots, even though the reverse levers \Vere in the 

reverse posiliun. 

The only way to reduce forward thrust under these abnormal circumstances is to move 

the reverse levers to the stowed position. However, moving the reverse levers to the stowed 

position would be counterintuitive to a pilot who was trying to reject a takeoff by applying 

maximum reverse thrust. Initially, flight crewmembers trying to slow the airplane would likely 

think that they are receiving the reverse thrust that they commanded until they realize that the 

airplane is not slowing. Therefore, the NTSB recommends that the FAA require Learjet to 

change the design of the Learjet 60 thrust lever system in future-manufactured airplanes so that 

the reverse lever positions in the cockpit match the positions of the thrust reverser mechanisms at 

the engines when the thrust reversers stow. Once design changes are developed per Safety 

Recommendation A-09-55, the NTSB recommends that the FAA require Learjet 60 operators to 

retrofit existing airplanes so that the reverse lever positions in the cockpit match the positions of 

the thrust reverser mechanisms at the engines when the thrust reversers stow. 

Lcarjct 60 Thrust Reverser Indications 

Norma lly, six lights7-three for each engine- will illuminate on the forward instrument 

panel to indicate the status of the thrust reversers (see figure). Each bottom light (TR ARM) is 

green and indicates that prerequisites for reverse thrust exist, such as the availability of hydraulic 

pressure to deploy the engine thrust reversers. Two of the conditions that trigger the TR ARM 

ljghts and that would be apparent to the pilots were that (I) the squat switches sense that the 

a;rcraft is in ground mode, and (2) the engine power levers are in the idle positions. The 

TR ARM lights denote that the reverse levers can be moved upward if the pilot elects. Because 

these lights are normally on when the engines are at the idle position on the ground and go out 

whenever the engine power levers are moved to and from idle, the pilot can become conditioned 

to these lights going on and off during normal taxi. 

When the reverse levers are raised to the DEPLOY position, hydraulic pressure unlocks 

the engine thrust reverser doors, and, subsequently, t\vo amber lights (TR UNLOCK) wi ll 

illuminate ·to indicate that both thrust reverser doors are unlocked. When the amber 

TR UNLOCK lights illuminate, the green TR ARM lights extinguish. After the engine thrust 

reverser doors are fully deployed, two white lights (TR DEPLOY) illuminate, and the amber 

TR UNLOCK lights extinguish. 

6 A nose gear steering disconnect tone was heard on the CVR, which was an indication that the squat switch 

went to air mode. The alert was advisory, under the conditions in this accident; no pilot action was needed. 

7 On Learjet 60 airplanes, indicator lights for the left thrust reverser are located on the left side of the instrument 

panel (in front of the pilot), and lights for the right thrust reverser are on the right side (in front of the copilot). 
4 

Thrust reverser indicator lights 

Figure. Diagram of a Learjet 60's lights on the main annunciator panel. 

Source: Flight Safety International Lea~et 60 Pilot Training Manual, Volume 1, Revision 1. 

If, during a rejected takeoff~ there were an inadvertent thrust reverser stowage due to loss 

of the requirements for maintaining reverse thrust, the following indications would occur: 

• The white TR DEPLOY light(s) would extinguish, 

o The amber TR UNLOCK light(s) would illuminate momentarily, and 

o The green TR .ARJ.\tllight(s) would blink momentarily. 

8 

The only indication available to the pilots that the cockpit reverse levers and engine th rust 

reversers were not in agreement would be the pi lots' comprehension that neither of the 

TR DEPLOY lights was illuminated while the reverse levers were in the positions norma lly 

associated with reverse thrust. The NTSB concludes that, during a rejected takeoff, which 

requires quick and concentrated pilot actions, it may be difficult for a pilot to recognize the 

significance ofthe absence of reverse thrust indicator lights. 

In the March 2009 TFM revision, Learjet expanded its rejected takeoff procedure by 

advising that, if none of the engine annunciator lights for both reversers is iI I um ina ted, the 

reversers have stowed. Additionally, a note was added to clarify the normal sequencing of the 

annunciator lights when thrust reversers are deployed. The NTSB is concerned that Lea rjet 60 

airplanes still do not provide sufficient cues for pilots to be able to quickly recognize an 

inadvertent thrust reverser stowage (and resultant forward thrust) and then make timely decisions 

and act on them. In addition to having a system in which the reverse lever position matches th e 

engine thrust reverser position, similar, more modern airplanes have a visual indication that 

informs the fl ight crew.(especially the nonflying pilot whose hand most likely is not on the lever) 

that the reversers have inadvertently stowed. Therefore, the NTSB recommends that the FAA 

require Learjet to develop and install improved aural or visual cues on future-manufactured 

Learjet 60 airplanes that would allow pilots to recognize an inadvertent thrust reverser stowage 

s The MASTER CAUTION light may illuminate momentarily if the MASTER CAUTION is not inhibited 

during takeoff; inhibiting the MASTER CAUTION light is a normal part ofthe Learjet 60 takeoff procedure. 
5 

in a timely manner. Once improved aural or visual cues are developed per Safety 

Recommendation A-09-57, the NTSB recommends that the FAA require Learjet 60 operators to 

install those cues on existing Learjet 60 airplanes. 

Inadvertent Thrust Reverser Stowage Procedure 

During initial certification of Lemjet 60 airplanes, Learjet developed an abnormal 

procedure in the event of an inadvertent thrust reverser stowage. Following a January 14, 2001, 

Learjet 60 accident, 

9 Lear jet amended the procedure; it is now an emergency procedure titled 

"Inadvertent Stow of Thrust Reverser After a Crew-Commanded Deployment." The procedure, 

located in the Learjet 60 Crew Checklist and in the Quick Reference Handbook (QRH), states in 

part: 

INADVERTENT STOW OF THRUST REVERSER AFTER A CREWCOMMANDED DEPLOYMENT 

1. Maintain control with rudde1; aileron, nose wheel steering & brakes 

2. Both Thrust Reverser Levers ........................ STOW{JOJ 

Steps 1 and 2 listed above are contained in a hatched box in the QRH indicating that the steps are 

to be performed by memory. 

The March 2009 TFM revision for Learjet 60 airplanes added a warning to this procedure 

and to the rejected takeoff procedure; the warning advises Learjet 60 operators that a damaged 

squat switch could potentially cause inadvertent thrust reverser stowage. The warning also 

d.escri bes engine power lever movements and light indications on the cockpit panel and on the 

engine ind ication system panel that result from the damaged squat switch and states that, if a 

d_amaged squat switch (or its fai lures) causes inadvertent thrust reverser stowage resulting 111 

fo rward thrust, then the thrust reverser levers must be stowed immediately. 

After this accident, investigators interviewed numerous pilots and instructors and found 

that the Inadvertent Stow of Thrust Reverser procedure was included during initial traini ng on 

the airplane. However, pilots and instructors said that the inadvertent stowage scenario was 

usually taught during landing phases rather than during takeoff phases. Another example of 

damaged squat switch wiring causing inadvertent thrust reverser stowage on takeoff occurred in 

June 1998. According to a voluntary pilot report submitted to the National Aeronautics and 

9 On January 14, 2001, a Learjet 60 registered to and operated by Ark-Air, Inc., collided with deer shortly after 

touchdown at Troy Municipal Airport, Troy, A labama, continued down the runway •vith tires smoking, veered off 

the right side of the runway, and impacted a ditch before bursting into flames. According to the pilots, the engine 

thrust reversers failed to operate when engaged. A sound spectrum study conducted by the NTSB indicated that 

engine thrust increased from 82.4 to 90.4 percent during the landing rollout and that the thrust reversers experienced 

an inadvertent stowage. Examination of the landing gear found all three gears collapsed and deer fur lodged in the 

squat switch on the left main landing gear. More information about this incident, ATLO lF A021, is available on the 

NTSB's website at <http://www.ntsb.gov/ntsb/queJy .asp>. As a result of this event, Learjet changed the squat 

switch circuitry to prevent inadvertent thrust reverser stowage after an airplane had taken off and flown, but the 

design change did not prevent an inadvertent stowage from occurring during a rejected takeoff. 

10 Moving both thrust reverser levers to stow would reduce commanded thrust to idle. 
6 

Space Administration's aviation safety reporting system, in the June 1998 event, the engine 

thrust reverser system was rendered inoperative due to damage to the squat switch system. In this 

event, a Learjet 60 experienced a failure of both right main tires during takeoff from Washington 

Dulles International Airport, Chantilly, Virginia. The tire failure resulted in the disintegration of 

the right main brake assembly, which severed the hydraulic lines and electric connections to the 

antiskid system and the squat switch system. The NTSB concludes that ~raining for inadvertent 

stowage of thrust reversers during only landing phases is insufficient to prepare pilots for this 

situation during rejected takeoff, when the airplane has greater acceleration energy. Therefore, 

the NTSB recommends that the FAA require that all Learjet 60 pilots receive training, for takeoff 

as well as landing phases of flight, on recognizing an inadvertent thrust reverser stowage, 

including the possibility that the stowage can occur when the requirements for deploying thrust 

reversers are not fully met, such as when the air/ground sensor squat switch circuits are 

damaged. Pilots must be aware that this can result in forward thrust even when the reverse levers 

are in the reverse thrust position. 

Similarly Designed Raytheon Hawker 1000 E ngine Installation 

The NTSB is aware that the engine installation for Raytheon Hawker 1000 business jets 

shares numerous similarities with the engine installation for Lea1j et 60 airplanes. Both airplane 

models use Pratt & Whitney PW305 engines and have similarities in the electronic engine 

controls, thrust reverser systems, and indications. Because of the similarities, the NTSB 

recommends that the FAA evaluate the design of the thrust reverser controls and indications in 

Raytheon Hawker 1000 business jets for potential thrust reverser failure modes that are similar to 

those identified in Lemjet 60 airplanes and implement necessary changes. 

Therefore, the National Transportation Safety Board recommends that the Federal 

Av iation Administration: 

Require Lea1jet to change the design of the Lemjet 60 thrust lever system in 

future-manufactured airplanes so that the reverse lever positions in the cockpit 

match the positions of the thrust reverser mechanisms at the engines when the 

thrust reversers stow. (A-09-55) 

Once design changes are developed per Safety Recommendation A-09-55, require 

Lemj et 60 operators to retrofit existing airplanes so that the reverse lever positions 

in the cockpit match the positions of the thrust reverser mechanisms at the engines 

when the thrust reversers stow. (A-09-56) 

Req uire Learjet to develop and install improved aural or visual cues on futuremanufactured Lear jet 60 airplanes that would allow pilots to recognize an 

inadvertent thrust reverser stowage in a timely manner. (A-09-57) 

Once improved aural or visual cues are developed per Safety 

Recommendation A-09-57, require Lea1j et 60 operators to install those cues on 

existing Learjet 60 airplanes. (A-09-58) 
7 

Require rhat all Lea1jet 60 pilots receive training, for takeoff as well as landing 

phases of flight, on recognizing an inadvertent thrust reverser stowage, including 

the possibility that the stowage can occur when the requirements for deploying 

thrust reversers are not fully met, such as \Nhen the air/ground sensor squat switch 

circuits are damaged. (A-09-59) 

Evaluate the design of the thrust reverser controls and indications in Raytheon 

Hawker I 000 business jets for potential thrust reverser failure modes that are 

similar to those identified in Lea1jet 60 airplanes and implement necessary 

changes. (A-09-60) 

In response to the recommendations in this letter, please refer to Safety 

Recommendations A-09-55 through -60. If you would like to submit your response electronically 

rather than in hard copy, you may send it to the following e-mail address: 

correspondence@ntsb. Q:OV. If your response includes attachments that exceed 5 megabytes, 

please e-mai I us asking for instructions on hov.r to use our Tumbleweed secure mailbox 

procedures. To avoid confusion, please use only one method of submission (that is, do not submit 

both an electronic copy and a hard copy of the same response letter). 

Acting Chairman ROSENKER and Members HERSMAN, HIGGINS, and SUMWALT 

concurred with these recommendations. 

[Original Signed} 

By: Mark V. Rosenker 

Acting Chairman