September 2005

NASA/TM-2005-213914

Small Aircraft Transportation System, Higher

Volume Operations Concept: Off-Nominal

Operations

Terence S. Abbott

Booz Allen Hamilton, McLean, Virginia

Maria C. Consiglio, Brian T. Baxley, Daniel M. Williams, and Sheila R. Conway

Langley Research Center, Hampton, Virginia
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September 2005

NASA/TM-2005-213914

Small Aircraft Transportation System, Higher

Volume Operations Concept: Off-Nominal

Operations

Terence S. Abbott

Booz Allen Hamilton, McLean, Virginia

Maria C. Consiglio, Brian T. Baxley, Daniel M. Williams, and Sheila R. Conway

Langley Research Center, Hampton, Virginia
Available from:

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS)

7121 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161-2171

(301) 621-0390 (703) 605-6000

Acknowledgments

The authors gratefully acknowledge the significant contributions of the many members of the research

team, from Government and Industry that were required to develop this concept. Deserving of credit are

Catherine Adams, Jennifer Murdoch, and Victor Carreno, as well as the contractor counterparts, from

Raytheon, James Sturdy; and from the National Institute of Aerospace, Cesar Munoz. Many other persons

whose names are not mentioned here have contributed significantly, and the authors express their

sincerest thanks. The authors are only reporting the results of this effort; the research team members are

what made this report possible.
iii

Table of Contents 

Nomenclature...............................................................................................................................................iv

1.0 Introduction.............................................................................................................................................1

2.0 Background.............................................................................................................................................1

2.1 Normal HVO Operations .....................................................................................................................1

2.2 Conflict Detection and Alerting...........................................................................................................6

2.3 Prototype Aircraft Multi-Function Display..........................................................................................6

3.0 Off-Nominal Operations .........................................................................................................................9

3.0 Off-Nominal Operations .........................................................................................................................9

3.1 Off-Nominal Categories.......................................................................................................................9

3.2 Implementation Considerations .........................................................................................................10

3.3 Routine Off-Nominal Procedures ......................................................................................................12

3.3.1 Pilot Cancellation of an Approach Request .................................................................................12

3.3.2 Change of Approach Direction ....................................................................................................13

3.3.3 Pilot Cancellation of a Departure Request ...................................................................................13

3.3.4 Leading Aircraft Conducting a Circle-to-Land ............................................................................14

3.4 Procedural Deviations........................................................................................................................14

3.4.1 Aircraft Returning to an Incorrect Missed Approach Holding Fix ..............................................14

3.4.2 Loss of Aircraft-To-Aircraft Spacing on Approach .....................................................................15

3.4.3 Unable to Use an Assigned IAF or MAHF ..................................................................................15

3.5 Equipment Malfunction Procedures...................................................................................................15

3.5.1 Loss of ADS-B Output on an Arriving SATS Aircraft................................................................15

3.5.2 Loss of ADS-B or APDLC Output on a Departing SATS Aircraft .............................................16

3.5.3 Loss of ADS-B Input on an Arriving SATS Aircraft...................................................................16

3.5.4 Loss of ADS-B or APDLC Input on a Departing SATS Aircraft ................................................17

3.5.5 Loss of AMM Output...................................................................................................................17

3.5.6 Loss of AMM Reception by a Single Aircraft .............................................................................18

3.5.7 Loss of Voice Communications ...................................................................................................18

3.6 Emergency Procedures.......................................................................................................................19

3.6.1 Priority Landing Request from an Aircraft with an Approach Sequence.....................................19

3.6.2 Priority Landing Request from a Departing Aircraft ...................................................................20

4.0 Summary...............................................................................................................................................24

5.0 References.............................................................................................................................................26
iv

Nomenclature 

ADS-B: Automatic Dependent Surveillance - Broadcast 

AMM: Airport Management Module 

APDLC: Airport-Pilot Data Link Communications 

ATC: Air Traffic Control 

ATIS: Automatic Terminal Information Service 

AWOS: Automated Weather Observing System 

CD&A: Conflict Detection and Alerting 

CD&R: Conflict Detection and Resolution 

CTAF: Common Traffic Advisory Frequency 

D-ATIS: Digital ATIS 

FAF: Final Approach Fix 

GPS: Global Positioning System 

HVO: Higher Volume Operations 

IAF: Initial Approach Fix 

IF: Intermediate Fix 

IFR: Instrument Flight Rules 

IMC: Instrument Meteorological Conditions 

MAHF: Missed Approach Holding Fix 

MFD: Multi-Function Display 

NAS: National Airspace System 

NNO: No New Operations 

PA: Pilot-Advisor 

PFD: Primary Flight Display 

RNAV: Area Navigation 

SATS: Small Aircraft Transportation System 

SCA: Self-Controlled Area 

TTA: Time To Approach 

VFR: Visual Flight Rules 
Abstract 

This document expands the Small Aircraft Transportation System 

(SATS) Higher Volume Operations (HVO) concept to include off-nominal 

conditions. The general philosophy underlying the HVO concept is the 

establishment of a newly defined area of flight operations called a SelfControlled Area (SCA). During periods of poor weather, a block of 

airspace would be established around designated airports where 

procedural separation is currently employed, i.e. airports with no tower 

and limited or no radar services available. Aircraft flying enroute to a 

SATS airport would be on a standard instrument flight rules flight 

clearance with Air Traffic Control providing separation services. Within 

the SCA, pilots would take responsibility for separation assurance 

between their aircraft and other similarly equipped aircraft. Previous 

work developed the procedures for normal HVO operations. This 

document provides details for a number of off-nominal and emergency 

procedures for situations that could be expected to occur in a future 

SCA. 

1.0 Introduction 

The intent of this document is to expand the Small Aircraft Transportation System (SATS) Higher 

Volume Operations (HVO) operational concept (refs. 1-4) to include a set of off-nominal operations, e.g., 

the failure of an airborne system normally required for a HVO operation. In this regard, this document 

will describe HVO procedures to address off-nominal operations, procedural deviations, equipment 

failures, and aircraft emergencies with a focus on safety and simplicity in the development of these 

procedures. In addition, because equipment design and equipment failure are highly interrelated with the 

development of off-nominal procedures, a specific equipment design will be discussed in this document. 

A major underlying assumption in the development of this document was that only reasonable failures 

and operational errors (i.e., failures and errors that had a practical expectation for occurrence) would be 

addressed. Hence, while the list of off-nominal conditions in this paper is not complete, it does cover a 

wide range of cases. The major design goals for these procedures were to minimize procedure and 

equipment changes relative to the normal procedures that were defined in ref. 1 while minimizing the 

level of system criticality (ref. 5). 

2.0 Background 

2.1 Normal HVO Operations 

The general philosophy underlying the SATS HVO operational concept is the establishment of a 

newly defined area of flight operations called a Self-Controlled Area (SCA). During periods of poor 

weather, a block of airspace would be established around designated airports where procedural separation 

is currently employed by Air Traffic Control (ATC), i.e. airports with no tower and limited or no radar 

services available. Aircraft flying enroute to a SATS airport would be on a standard instrument flight 

rules (IFR) clearance with ATC providing separation services. Within the SCA, pilots would take 

responsibility for separation assurance between their aircraft and other similarly equipped aircraft. Note, 

however, that while pilots would be required to take responsibility for self-separation within the SCA, 
2

they would not be required or allowed to take responsibility for establishing the sequence of their arrivals 

within the SCA. This concept would take advantage of a proposed ground-based automation system, 

called an Airport Management Module (AMM), which would provide sequencing information to pilots 

for safe and improved operations. The AMM would typically be located at the airport and would make 

these assignments based on calculations involving aircraft performance, aircraft position information, 

winds in the terminal area, missed approach requirements, and a set of predetermined operating rules for 

the SCA. This sequence assignment process supports actions and decisions made by ATC in that it 

sequences only those aircraft at the lowest altitude approaching the Initial Approach Fixes (IAFs), 

allowing ATC to control the sequence order of the arriving aircraft. This process allows the controller the 

flexibility to resolve issues unknown to the AMM (e.g., crossing airways, weather, and aircraft holding). 

A plan view graphic depicting a generic SCA is shown in figure 1. The SCA would be similar in 

concept to a Class E surface area and is similar to the proposal by Conway and Consiglio in reference 2. 

The waypoints could be existing waypoints for a generic Global Positioning System (GPS) T approach. 

In this concept, the outboard IAFs on the T (e.g., ANNIE and CATHY) would be used for all arrivals. 

These fixes would also be used as the missed approach holding fixes (MAHF). During low traffic 

conditions, an arriving aircraft could fly directly to an IAF at the lowest appropriate IFR altitude and 

upon reaching the IAF, begin an approach operation. During periods of higher traffic conditions, the 

holding pattern in the SCA would be used to delay aircraft while they are waiting for appropriate aircraftto-aircraft separation prior to initiating the approach and landing. Arriving aircraft would enter at the top 

of the IAF holding pattern and drop down in 1,000-foot increments as the altitude below becomes clear, 

until they reach the initial approach altitude. At that time, the aircraft would self-separate along the 

approach path for landing. The profile view in figure 2 shows one of these arrival fixes and helps 

illustrate the holding pattern above the IAF. Note also that the shape of the SCA is similar to a Class C 

airspace design, but offset on the approach-side of the airport. Additionally, the shape of the SCA may 

also be tailored to fit the geometry of local airspace constraints. The outrigger IAFs on the opposite T 

could be used as the departure fixes. 

Figure 1. Plan view example of a Self-Controlled Area. 
3

Figure 2. Profile view example of a Self-Controlled Area. 

As noted previously, the AMM would consist of a ground-based automation system, typically located 

at the airport. The AMM would not be an automation of the ATC function but would be more of a simple 

counter that issues sequence information based on a set of predetermined rules. The AMM would rely on 

aircraft position information provided through a ground-based Automatic Dependent Surveillance 

Broadcast (ADS-B) receiver to manage the operations within the SCA. Aircraft would be expected to 

contact the AMM via data link (Airport-Pilot Data Link Communications, APCLC) and request landing 

sequence information. The AMM would then provide either a notification of which airplane the pilot 

would follow (if there was an airplane in the sequence ahead of the pilot) or inform the pilot that he 

cannot initiate the operation (e.g., enter the SCA) and provide him with a notification of the delay to 

expect before the operation can begin. What is unique to this concept is that ATC has implicit control of 

the arrival sequencing. This implicit control occurs because the AMM only accepts vertical entries into 

the SCA from aircraft flying immediately above the SCA (i.e., at the lowest IFR altitude above the SCA 

vertical boundary). This design could provide ATC with a relatively low workload and seamless means 

for controlling IFR entries into the SCA. In this concept, ATC directs aircraft to the appropriate IAF; the 

AMM provides the aircraft with an approach sequence; and the pilot follows the sequence for the 

approach and landing. 

In addition to its other calculations, the AMM must also assure that there would be available missed 

approach airspace for each aircraft arriving in the SCA. Since it must be assumed that every approach 

may result in a missed approach and since there would not be an active controller involved in SCA 

operations (who could respond in real time with unique missed approach instructions), each aircraft 

entering the SCA would be given specific missed approach information by the AMM as it enters the 

airspace. This technique would keep the ground-based automation relatively simple and less critical to 

the operational concept. However, it would mean that the total number of operations would be 

constrained by the number of unique missed approach locations that could exist within the SCA. For the 

SCA shown in figures 1 and 2, there are four missed approach holding options (two holding altitudes at 

each MAHF), therefore there are a total of four approach operations allowed at one time in this version of 

a SCA. Again, it is expected that this design would be modified for specific airport and airspace 

configurations. Also note, however, that designs with significantly more missed approach fixes may not 

significantly increase the number of allowable landing operations. 

For the generic SCA shown in figures 1 and 2, there are four missed approach positions, two at 

ANNIE and two at CATHY. Therefore, there would be a total of four approach operations allowed at one 

time in the generic SCA. From this maximum of four operations, exclusive of departure operations, a set 

of implementation and operating rules were developed. The normal SCA operating rules are as follows: 

- No more than four concurrent arrival operations are allowed in the SCA. 

- Simultaneous entries are not allowed at a single IAF. 
4

- Entry is granted only if no other aircraft on approach is assigned to that fix as their MAHF. 

- Entries may not result in the assignment of more than two aircraft to a specific fix, with the 

assignment as either an IAF or as a MAHF. 

- Vertical entries (descending into the SCA while in the arrival holding pattern) are only allowed at the 

IAFs from the lowest IFR altitude above the SCA. 

- Upon entering the SCA at an IAF, aircraft are to go to the lowest available altitude and then continue 

to descend as altitudes below them become available. 

- Alternating MAHFs are given to sequential aircraft (e.g., the first aircraft is given ANNIE, the second 

aircraft is given CATHY, the third aircraft is given ANNIE, etc.). Note that for operational efficiency 

reasons, if there were no other landing aircraft (i.e., aircraft with approach sequences) in the SCA, the 

first arriving aircraft would be assigned a "same-side" MAHF (e.g., if the arrival fix is ANNIE, the 

MAHF will be ANNIE). An example approach chart with ANNIE as the MAHF is given in figure 3. 

- When proceeding to a holding fix on a missed approach, aircraft are to climb to the lowest available 

altitude (e.g., the first aircraft heading to ANNIE climbs to 2000 feet, the next aircraft going to 

ANNIE climbs to 3000 feet). 

- Aircraft operating in the SCA must be able to climb at 300 feet per mile (required for obtaining the 

required vertical separation at a MAHF if the lower altitude is occupied). 

It is also noteworthy that airports would only need to make relatively minimal infrastructure 

investments to increase their ability to sustain operations during periods of IMC. Airports would be 

expected to have weather reporting capability (e.g., Automated Weather Observing System - AWOS) and 

would need to install an AMM, a ground-based ADS-B receiver, and have a data link capability. AWOS 

input into the AMM may also be needed to assist the AMM to determine the appropriate instrument 

procedure (i.e., the appropriate landing direction). 

For this operational concept to be viable, a link between the AMM and ATC would be required. This 

link would be necessary to enable ATC to terminate and subsequently re-enable HVO operations when 

necessary to accommodate non-HVO operations (e.g., normal IFR operations). This link would also be 

necessary to efficiently enable HVO departure operations that would transition into traditional IFR 

airspace. Additionally, if controllers had access to the SCA status information, this could facilitate air 

traffic management. For example, if controllers knew that the SCA was not currently accepting aircraft 

(because the SCA was full), and that there would be a 20-minute delay at the airport, they could begin 

planning for that delay in advance. This information could then be provided to arriving aircraft by ATC 

or possibly broadcast on ATIS-like transmission. 

Since the SATS project is focused on achieving a realistic, operationally deployable system for the 

2010 timeframe, this concept emphasized integration with the current and the planned near-term National 

Airspace System (NAS). As a result, the design approach focused on simplicity from both a procedural 

and systems requirements standpoint. It was further assumed that any additional ATC workload must be 

minimized and that enroute procedures would be as similar to today’s system as possible. This concept is 

based on a distributed decision-making environment that would provide pilots with the necessary 

procedures, airborne systems, traffic awareness, and aircraft sequence information to enable safe 

operations within the SCA while minimizing the requirements for ground support tools. Because this is a 
5

distributed decision-making environment, much of the decision-making responsibility would be left with 

the pilot, as it is today with visual flight rules (VFR) operations into non-towered airports. Finally, the 

overall philosophy in the development of the HVO operational procedures was to emphasize simplicity 

and operational safety as major aspects in the design. The details of these procedures for normal 

operations are provided in ref. 1. 

Figure 3. Example approach chart. 

Missed Approach: Climbing right turn to lowest 

available (2000 or 3000) via LNAV path to CATHY 

and hold. 

SATS RNAV (GPS) RWY 3 CATHY

MELFA/ACCOMACK COUNTY (MFV) 

124

o

304

o

124

o

304

o

1500

034

o

(5)

2000

304

o

(5)

2000

124o

(5)

Rwy ldg 4999

TDZE 47

Apt Elev 47

APP CRS

034 0

AWOS-3

118.175

NORFOLK APP CON

126.05

JAGNO

CATHY

JAGNO 

(MAF and 

Threshold)

MELFA 

(FAF)

(IAF) 

CATHY 

(IAF) 

ANNIE 

(IF) 

UCGEL 

SATS RNAV (GPS) RWY 3 CATHY

MELFA/ACCOMACK COUNTY (MFV) 

MELFA, VIRGINIA

MELFA, VIRGINIA

SATS Equipped Only

GPS or RNP-0.3 required

DME/DME RNP .3 NA 

MELFA

UCGEL

2000

1500

0340

3.000

TCH 40

CATEGORY

LNAV MDA

CIRCLING NA

440-1 393 (400-1) 440-1 1/4 

393 (400-1 1/4)

A B C D

5 NM 4.5 NM 0340 TO

RWY 3

TDZE

47

5004 X 100 REIL Rwys 3 and 21 L

MIRL Rwy 3-21 L

ELEV 47

127 +

143 .

.

. 136 +

SATS Self 

Controlled 

Area . 264

. 515

. 349

331 + .

374 .

3000

2000

Research Only – Not for Navigation

UNICOM

122.8 (CTAF) L

Missed Approach: Climbing right turn to lowest 

available (2000 or 3000) via LNAV path to CATHY 

and hold. 

SATS RNAV (GPS) RWY 3 CATHY

MELFA/ACCOMACK COUNTY (MFV) 

124

o

304

o

124

o

304

o

1500

034

o

(5)

2000

304

o

(5)

2000

124o

(5)

Rwy ldg 4999

TDZE 47

Apt Elev 47

APP CRS

034 0

AWOS-3

118.175

NORFOLK APP CON

126.05

JAGNO

CATHY

JAGNO 

(MAF and 

Threshold)

MELFA 

(FAF)

(IAF) 

CATHY 

(IAF) 

ANNIE 

(IF) 

UCGEL 

SATS RNAV (GPS) RWY 3 CATHY

MELFA/ACCOMACK COUNTY (MFV) 

MELFA, VIRGINIA

MELFA, VIRGINIA

SATS Equipped Only

GPS or RNP-0.3 required

DME/DME RNP .3 NA 

MELFA

UCGEL

2000

1500

0340

3.000

TCH 40

CATEGORY

LNAV MDA

CIRCLING NA

440-1 393 (400-1) 440-1 1/4 

393 (400-1 1/4)

A B C D

5 NM 4.5 NM 0340 TO

RWY 3

TDZE

47

5004 X 100 REIL Rwys 3 and 21 L

MIRL Rwy 3-21 L

ELEV 47

127 +

143 .

.

. 136 +

SATS Self 

Controlled 

Area . 264

. 515

. 349

331 + .

374 .

3000

2000

Research Only – Not for Navigation

UNICOM

122.8 (CTAF) L
6

2.2 Conflict Detection and Alerting 

As noted in the development of the normal operational procedures for the SCA, an explicit design 

decision was made in that neither conflict detection and alerting (CD&A) nor conflict detection and 

resolution (CD&R) would be required as a primary means for aircraft separation in conducting HVO. 

That is, the HVO procedures, with the supporting AMM design and relatively simple flight displays, 

would provide the primary means for aircraft-to-aircraft separation within the SCA. It was assumed, 

however, that either CD&A or CD&R would be required as a secondary means for operational safety. 

Given this, the inherent nature of off-nominal situations will probably require an onboard conflict 

detection system to obtain an operationally viable level of safety. 

2.3 Prototype Aircraft Multi-Function Display 

The underlying functionality and display formats of a modern multi-function display (MFD), 

representative of a current-generation GPS moving map display, were assumed as the implementation 

basis for the SATS HVO concept. A basic map-page layout for this generic MFD is shown in figure 4. 

Major functions and display items assumed for the map portion of the MFD are: 

- A track-up, moving map display that includes both geographic and navigation information. 

- Aircraft-centered and aircraft-offset formats. 

- Adjustable map range scales. 

- Programmable bezel buttons. 

- Feature-select knobs. 

Figure 4. Generic MFD map layout. 

Feature select knob, 

function specific 

Feature select knob, 

primary functions 

AMM-procedure 

display window 

Pilot Advisor window 

Programmable bezel 

buttons 
7

In addition to the navigation map information, the MFD would provide traffic information (ref. 6), 

HVO-specific alerting information, and Airport-Pilot Data Link Communications (APDLC) messages. 

APDLC messages could provide AMM messages as well as general airport information, such as Digital 

Automatic Terminal Information Service (D-ATIS). Note that APDLC is a two-way, addressed data link 

that would function in a manner similar to a CPDLC system (ref. 7). 

The MFD would also include a pilot procedure tool, unique to the HVO concept. This tool, called the 

Pilot-Advisor (PA), would provide an automated HVO-specific checklist to the pilot relative to the 

current state of the aircraft and other surrounding traffic. Effectively, the PA, would provide prompts in 

the PA window to the pilot regarding the next appropriate procedural step for the current HVO 

procedure. The PA window would only display one message at a time, with that message being the oldest 

message with the highest priority. Table 1 lists the proposed messages, with priority level 1 as a higher 

priority than priority level 0. For example, the “Monitor Path” (blue, priority level 1) takes precedence 

and would overwrite the “OPEN: 2000” message (black, priority 0). The message text color would be 

consistent with alerting standards (ref. 8). The prototype messages for the PA information, displayed in 

the PA window on the MFD, are provided in Table 1. Unlike the SATS HVO requirement for CD&A or 

CD&R, the HVO concept does not require the use of a PA, although preliminary tests with subject pilots 

have found it to be highly desirable. 

Alerting information, provided in an alert window on the MFD map, along with any appropriate audio 

cues, would also be provided via the MFD. Alerting information would include the following: 

- The availability of any new broadcast message: e.g., AWOS, D-ATIS, or AMM broadcast data. 

- The reception of any new AMM instruction addressed to the aircraft, e.g., entry notification. 

- A new PA message. 

- Traffic conflict messages. 

This MFD implementation, along with the PA tool, is but one possible means for providing an airborne 

capability to support the HVO concept. 
8

Table 1. Pilot-Advisor (PA) Messages 

Message definition Example 

message 

Priority 

level 

The pilot is entering the SCA without an entry notification 1 

The pilot is entering the SCA at the wrong IAF. 1 

“Open altitude” informs the pilot of the next altitude that is required for the current 

procedure and indicate that no other HVO aircraft is occupying that altitude. This 

message example informs the pilot that the 3000 ft altitude slot is open (available). 

0 

The pilot has climbed or descended beyond the open (available) altitude. This 

message would be displayed on the second line of the PA window as a modifier to 

the instruction displayed on the first line. 

1 

If an operation is pending but has not occurred after a predetermined time due to an 

unexpected delay by the pilot, a "proceed now" prompt will be added to the PA 

message. This message will also be associated with an alert. 

 1 

Time-To-Approach (TTA) defines when the aircraft may leave the IAF with the 

appropriate spacing behind the aircraft it will be following. The example is 1 minute, 

32 seconds before approach initiation. 

0 

This message shows the pilot that the approach may be initiated. 0 

This message shows that the separation distance from the pilot’s aircraft to the 

preceding approach aircraft is below the nominal value (for either an approach or a 

departure) and that the pilot should reduce speed. 

1 

The pilot is flying faster than the nominal approach speed. 1 

The pilot is flying slower than the nominal approach speed. This message is 

inhibited if a "too close" message has been issued. 

1 

The pilot is flying off of the approach path. 1 

The pilot is the second aircraft conducting a missed approach to a common MAHF, 

and he is overtaking the preceding missed approach aircraft. An expedited climb to 

3000 ft is required in this example; this information would be shown on the second 

line of the message window. 

1 

The pilot is going to the wrong MAHF. 1 

This message shows that a departure may be initiated. It is displayed when the pilot 

is ready for takeoff and there is sufficient separation between both arriving and 

departing HVO aircraft for an HVO departure operation to be performed. 

0 

The pilot is flying the wrong departure procedure. 1 

NO SEQUENCE

EXIT SCA

WRONG IAF

OPEN: 3000

OPEN: 3000

MONITOR ALT

TTA: 1:32

OPEN: 2000

PROCEED NOW

OPEN: APPR

TOO FAST

CHECK SPEED

TOO SLOW

CHECK SPEED

OPEN: 3000

CLIMB NOW

WRONG MAHF

OPEN: DEPART

WRONG DP

MONITOR PATH

TOO CLOSE

REDUCE SPD
9

3.0 Off-Nominal Operations 

The development of off-nominal operations created a set of procedures somewhat similar to today’s 

procedures. It was recognized that procedures cannot be written for every possible scenario, and that 

voice communication will sometimes be essential in safely concluding an off-nominal operation. 

Development of these proposed off-nominal operations still require a safety fault tree analysis and 

experiments to validate them. This papers offers one possible implementation, i.e., using a MultiFunction Display and a Pilot Advisor. However, other implementation schemes are possible, and the Pilot 

Advisor functionality is not a requirement of HVO. 

3.1 Off-Nominal Categories 

The off-nominal conditions that were identified for inclusion into the HVO procedures were classified 

into four categories: routine off-nominal operations, procedural deviations, equipment malfunctions, and 

aircraft emergency procedures. 

The routine off-nominal conditions that were identified included:

- A pilot cancellation of an approach request. 

- A change of landing approach direction. 

- A pilot cancellation of a departure request. 

- Leading aircraft conducting a circle-to-land operation. 

The procedural deviations that were identified included:

- An aircraft returning to an incorrect MAHF. 

- A loss of aircraft-to-aircraft spacing on approach. 

- The inability to use an assigned IAF or MAHF. 

The equipment malfunctions that were identified included:

- The loss of aircraft state data output on an arriving SATS aircraft. 

- The loss of aircraft state data output on a departing SATS aircraft. 

- The loss of aircraft state data input on an arriving SATS aircraft. 

- The loss of aircraft state data input on a departing SATS aircraft. 

- The loss of the AMM. 

- The loss of AMM reception by a single aircraft. 

- The loss of voice radio communication capability. 
10

The emergency conditions that were identified included the following:

- A priority-landing request from an aircraft with an approach sequence. 

- A priority-landing request from a departing aircraft. 

Examples of each of these two emergency conditions are shown in figures 5 and 6. Figure 5 is an 

example of a priority-landing request from an aircraft holding for an approach at ANNIE at 3000 ft. In 

this figure, the aircraft at the highest altitude has made a priority request and will follow the aircraft on 

final approach, landing ahead of the aircraft holding at the lower altitudes. Figure 6 is an example of a 

priority-landing request from a departing aircraft. This condition would occur if an aircraft conducting an 

HVO departure needed an unplanned, immediate return to the airport. In this figure, the departing aircraft 

(the right-most aircraft) has made the landing request and will land before the two aircraft on the farther 

holding patterns. 

The procedures that were developed to support these identified conditions are provided in the 

subsequent sections. 

Figure 5. Example of a priority-landing request. 

Figure 6. Example of priority landing request from a departing aircraft. 

3.2 Implementation Considerations 

The addition of off-nominal operations in this document, and the development of their operational 

procedures have, not surprisingly, led to some increase in the overall complexity of the concept required 

to support these operations. However, as in the development of the normal operational procedures, these 

Aircraft requesting 

priority 

Aircraft requesting 

priority 
11

new procedures were based, whenever possible, on similar existing procedures for VFR operations or 

non-radar, IFR operations. Also, with regard to VFR operations, it is worthwhile to reiterate that the 

normal operational procedures (ref. 1) allow for mixed operations of both SATS and VFR aircraft, where 

these operations are expected to be accommodated in a manner similar to today’s mix of IFR and VFR 

aircraft, i.e., the pilot is responsible to see and avoid other traffic (ref. 9). 

Also as noted previously, off-nominal operations, especially the detection of equipment failures, will 

require system-to-system periodic checks and some data retention outside of the AMM. As such, the 

following requirements were identified to support the off-nominal procedures. 

- Changes to the SCA state data information (performed in two phases) 

1. System-to-system (e.g., AMM to the aircraft via the APDLC) information exchange would 

require confirmation from the receiver back to the sender. 

2. A confirmation process within the aircraft would be required between the aircraft systems and 

pilot (e.g., the pilot alerted to a change responds with activation of a confirmation/accept button 

on the MFD). 

- Periodic AMM status messages to all participating HVO aircraft. 

- Periodic ADS-B reception messages from the AMM to participating HVO aircraft (after the AMM 

has received an ADS-B message from the aircraft, it would periodically reply with a message back to 

the aircraft noting that the aircraft’s ADS-B message has been received). This message is necessary to 

alert aircraft to a loss of their ADS-B output or APDLC input capabilities, and is also required prior to 

conducting a departure operation. 

- Prior to takeoff, departing HVO aircraft would require the reception of both an AMM normaloperation status message and an ADS-B reception message from the AMM. 

- Current SCA status information (e.g., the number of operations and aircraft identification) would be 

sent from the AMM. 

- Each participating aircraft would retain sequence data from the AMM on all surrounding SCA traffic. 

This information would be used by the pilots in situations when a reversion to pilot-to-pilot 

procedural separation is required due to the loss of aircraft state data information. These situations 

would be analogous to ATC situations upon the loss of ATC radar information. 

- Periodic AMM normal-operation status messages would be sent to ATC (e.g., the number of 

operations and aircraft identification). 

It is also important to note that while ADS-B would be the primary means for the dissemination of 

aircraft state data, the APDLC could be used to provide a secondary means for data exchange. Therefore, 

failures such as the loss of state data transmission are procedurally addressed only if all means of 

transmission have failed. 

This document only covers procedures unique to SATS HVO. Pilots are expected to use traditional 

procedures in managing situations that are not unique to HVO. Furthermore, today’s requirement for the 

use of voice communication and airmanship in handling emergencies will still be required in HVO. 
12

Also note that any situation that would require closing the airport, e.g., a single-runway airport with 

the runway closed due to an accident, would require all approach aircraft to conduct a procedure similar 

to Initiating a Departure from a Missed Approach, described in reference 1. 

3.3 Routine Off-Nominal Procedures 

3.3.1 Pilot Cancellation of an Approach Request 

It is envisioned that this procedure would be used when weather conditions within the SCA would be 

marginal VFR with the instrument approach operation transitioning to a visual approach. For a pilot to 

cancel an HVO approach, VFR conditions to the airport must exist (although the aircraft may remain on 

an IFR flight plan). 

Canceling aircraft: 

1. The pilot would select the “cancel approach” feature on the MFD. 

2. The MFD would send the cancellation request to the AMM. 

3. The AMM would mark the aircraft as a non-participating aircraft (e.g., it is assumed that the 

aircraft has transitioned to VFR). 

4. The AMM would send the cancellation notice to the canceling aircraft. 

5. The MFD would notify the pilot that his cancellation request was received by the AMM. 

6. If the canceling aircraft has not received an approach sequence (i.e., it was outside the SCA with 

a standby notification), the AMM would delete the aircraft from its request queue. 

7. If the aircraft had received an approach sequence: 

- The canceling pilot would announce the cancellation over the Common Traffic Advisory 

Frequency (CTAF). 

- The AMM would remove the canceling aircraft from the approach sequence. 

- The AMM would re-sequence the aircraft that followed the aircraft canceling HVO. 

- The AMM would send the new sequence information to all HVO aircraft. 

Other HVO aircraft: 

1. The MFD would identify the canceling aircraft as a non-participating aircraft. 

2. If the aircraft had an approach sequence that has been changed (i.e., re-sequenced by the AMM), 

the MFD would notify the SATS pilot to the changes in the approach information (e.g., new 

leading aircraft and/or MAHF). 
13

3. The MFD would inhibit all continuing-operations PA messages (e.g., OPEN 3000, OPEN 

APPROACH) until the pilot of the re-sequenced aircraft acknowledged the re-sequence. This 

acknowledgement could occur via a button-press on the MFD. 

Note that for this and all other procedures that require an information exchange (e.g., cancellation 

request or re-sequence data) between the pilot and the onboard system, an acknowledgement by the pilot 

would be required. As noted previously, this acknowledgement could occur via a button-press on the 

MFD. Similarly, an information exchange between the onboard system and the AMM would also require 

an underlying (system-to-system) data exchange confirmation (e.g., an acknowledgement). This 

acknowledgement could occur via a data link “handshake” between the two systems. 

3.3.2 Change of Approach Direction 

The determination of the active runway should probably be a function of ATC, which may require 

ATC support tools, better than a D-ATIS or AWOS, in supporting this determination. Additionally, pilots 

should be able to provide feedback and input into the decision regarding the selection of the approach 

direction and the active runway. Further research may be required to agree upon an appropriate means for 

providing this determination. 

It should be noted that normal changes of runway landing direction should be managed prior to aircraft 

being assigned approach sequences. That is, ATC should inhibit arrivals until all ongoing SCA 

operations have been completed, holding the new arrivals above the SCA until all current SCA operations 

have been completed. Also note that the SCA approach direction may not need to change if circle-to-land 

operations are used. Assuming that a change to the instrument approach direction must take place while 

aircraft are conducting SCA operations, the following should occur: 

1. The AMM should inhibit all new SCA operations and set the SCA status to no new operations 

(NNO). 

2. The AMM should notify ATC that the SCA is in an inhibit status. 

3. The AMM would notify ATC regarding the configuration change and identify all active HVO 

aircraft. 

4. All landing aircraft should either land or conduct a missed approach operation. 

5. Missed approach aircraft should contact ATC to obtain a clearance to the MAHF at the lowest 

IFR altitude above the SCA. 

6. At the completion of all HVO approach operations, which would occur when all aircraft have 

either landed or are no longer actively conducting SATS operations, the AMM would reconfigure 

the SCA for the new landing direction. 

7. Once all of these actions have occurred, ATC may allow the AMM to resume SCA operations. 

3.3.3 Pilot Cancellation of a Departure Request 

If a pilot cancels an SCA departure request, the following should occur: 
14

1. PA alerting would be inhibited for the canceling aircraft. 

2. All other aircraft would continue with their normal operations. 

3.3.4 Leading Aircraft Conducting a Circle-to-Land 

This situation would occur if the leading aircraft plans to conduct a circle-to-land operation. For this 

situation, the following procedure should be used: 

1. The pilot of the circle-to-land aircraft would select this function on the MFD. 

2. The MFD of the circle-to-land aircraft would send the circle-to-land information to include the 

intended landing runway to all HVO aircraft. 

3. Based on the received circle-to-land intent information, the following aircraft would have an 

additional distance or time interval added to the nominal spacing value for the approach spacing. 

Further development of this operation may be required. 

3.4 Procedural Deviations 

3.4.1 Aircraft Returning to an Incorrect Missed Approach Holding Fix 

This procedure addresses the problem of an HVO pilot attempting to fly an incorrect missed approach 

procedure for the instrument approach. Note that for a pilot to turn toward the wrong MAHF, the pilot 

would have already made the following errors: performed the incorrect missed approach procedure; 

ignored the MAHF identified in the MFD “to waypoint” data block; ignored the missed approach 

procedure depicted on the moving map display of the MFD (and any associated primary flight guidance 

information on the Primary Flight Display - PFD); and ignored the PA alert for an incorrect missed 

approach procedure. 

In the event that an aircraft does accidentally attempt to return to the wrong MAHF, the following 

procedure should be performed once the pilot recognizes the error (e.g., observes the correct MAHF 

name on the MFD): 

1. The pilot should make a call over CTAF announcing the problem. 

2. The pilot should contact ATC as soon as possible and announce the problem 

3. Due to the potential loss of separation with other aircraft on the instrument approach, this aircraft 

must not attempt to return to the assigned MAHF. The pilot should continue climbing along the 

errant missed approach path to an altitude above the SCA. 

4. The pilot should contact ATC and request an IFR clearance from ATC. If possible, this clearance 

should be obtained prior to departing the SCA. 
15

3.4.2 Loss of Aircraft-To-Aircraft Spacing on Approach 

An aircraft that is predicted to lose aircraft-to-aircraft spacing while on the approach and subsequently 

receives a loss-of-separation alert should do the following: 

1. Begin an immediate climb to its missed approach altitude. 

2. Fly the lateral path of the approach and subsequent missed approach. 

3. Fly the planned approach speeds (to maintain conformance for other SCA aircraft), where these 

speeds are either standard speeds for the aircraft or pre-selected by the pilot. 

3.4.3 Unable to Use an Assigned IAF or MAHF 

This condition may occur because of severe weather at the IAF or MAHF. 

If this situation occurs while still in ATC managed airspace, the pilot should coordinate with ATC to 

proceed to the other IAF or divert to another airport. 

If within the SCA, the pilot should climb above the SCA in the safest possible manner, avoiding 

obstacles, other aircraft, and the severe weather. During the climb, the pilot should notify ATC of the 

situation, noting that contacting ATC is a priority since the aircraft could be entering controlled airspace 

without a clearance. 

3.5 Equipment Malfunction Procedures 

3.5.1 Loss of ADS-B Output on an Arriving SATS Aircraft 

This situation would occur if an HVO aircraft had lost the capability to transmit its state data 

information via ADS-B. If this situation exists, the following should occur: 

Aircraft Without an Arrival Sequence: 

Part of the arrival sequencing process that the AMM performs is the confirmation of ADS-B state data 

output from the requesting aircraft. If the aircraft has not already been issued an arrival sequence, the 

AMM would attempt to confirm the aircraft’s ADS-B transmit capability (and all other output 

capabilities) prior to the sequence notification. If there is no ADS-B output, the aircraft would be notified 

of this condition and it would be denied an approach sequence. 

Aircraft With an Arrival Sequence and with APDLC Output:

If the aircraft has an approach sequence and subsequently loses its ADS-B output but still has APDLC 

capability, the following should occur: 

1. The AMM, noting the loss of the ADS-B signal from an aircraft, would inhibit all new SCA 

operations and would set the SCA status message to no-new-operations (NNO). 

2. The AMM would notify ATC that the SCA is in an inhibit status. 
16

3. The AMM, noting the loss of an ADS-B signal from an aircraft, would send that aircraft a “lost 

ADS-B output” message that could be displayed as an alert message on the MFD. The problem 

aircraft would then begin (or continue) transmitting its position data over the APDLC. This APDLC 

message would be broadcast to all aircraft in the SCA. 

4. The AMM would resume normal operations after the problem aircraft has landed and would also 

set the SCA status appropriately. 

Aircraft With an Arrival Sequence and without APDLC Output:

If the aircraft has an approach sequence and subsequently loses both its ADS-B output and its APDLC 

capability, the following should occur: 

1. The AMM, noting the loss of an ADS-B signal from an aircraft (and all other output capability), 

would inhibit all new SCA operations and set the SCA status message to no-new-operations 

(NNO). 

2. The AMM would notify ATC that the SCA is in an inhibit status. 

3. The AMM would send all aircraft a “lost signal” message via the APDLC, identifying the aircraft 

that had lost its transmission capability. 

4. All aircraft that were conducting approach operations would revert to procedural separation using 

CTAF and continue the approach operations using their original sequence assignments. 

5. Departure operations would be inhibited until the aircraft with the problem lands. 

6. A notification to the AMM that the problem aircraft has landed or has departed the SCA would be 

accomplished via a ground-based message from ATC. 

3.5.2 Loss of ADS-B or APDLC Output on a Departing SATS Aircraft 

Prior to conducting an SCA departure operation, aircraft would perform an ADS-B and APDLC check 

with the AMM. It is envisioned that if a successful link check could not be performed, the PA would 

inform the pilot that an HVO departure was not possible. In this instance, this departing aircraft would be 

required to revert to unequipped operations (ref. 1). 

3.5.3 Loss of ADS-B Input on an Arriving SATS Aircraft 

This situation would occur if an HVO aircraft had lost the capability to receive ADS-B information 

from other SCA aircraft. If this situation takes place, the following should occur: 

Aircraft Without an Arrival Sequence:

Part of the arrival sequencing process that the AMM performs is the confirmation of ADS-B state data 

input to the requesting aircraft. If the aircraft has not already been issued an arrival sequence, the AMM 

would attempt to confirm the aircraft’s ADS-B reception capability (and all other input capabilities) prior 

to the sequence notification. If there were no ADS-B inputs, the aircraft would be denied an approach 

sequence. 
17

Aircraft With an Arrival Sequence but with APDLC Input:

If the aircraft has an approach sequence and subsequently lost its ADS-B reception capability but still 

had APDLC capability, the following should occur. 

1. The aircraft with the equipment problem would notify the AMM of the loss of ADS-B reception. 

2. If all SCA aircraft were not already broadcasting their position data via APDLC, the AMM would 

request this transmission of state data via APDLC from all participating aircraft. 

3. The aircraft with the equipment problem would use the APDLC-received state data as necessary. 

Aircraft With an Arrival Sequence and without APDLC Input:

If the aircraft has an approach sequence and subsequently loses its ADS-B input and its APDLC 

capability, the following should occur. 

1. The aircraft with the equipment failure would notify the AMM of the loss of ADS-B reception 

capability. Lack of a periodic status message via APDLC from an aircraft could also cause the 

AMM to initiate this event. 

2. The AMM would inhibit all new SCA operations and set the SCA status message to 

no-new-operations (NNO). 

3. The AMM would notify ATC that the SCA is in an inhibit status. 

4. The AMM would send all aircraft an “unable to receive” message via the APDLC, identifying the 

aircraft that had lost its reception capability. 

5. All aircraft conducting approach operations would revert to procedural separation using CTAF 

and continue the approach operations using their original sequencing assignments. 

6. The AMM would resume normal operations after the problem aircraft has landed and would set 

the SCA status appropriately. 

3.5.4 Loss of ADS-B or APDLC Input on a Departing SATS Aircraft 

Part of the departure process that the AMM performs is the confirmation of ADS-B state data input to 

the requesting aircraft. The AMM would attempt to confirm the aircraft’s ADS-B reception capability 

(and all other input capabilities). If this confirmation fails, this aircraft would be required to revert to 

unequipped operations. 

3.5.5 Loss of AMM Output 

The AMM would send a periodic operational status message to ATC and to all proximate aircraft via 

the APDLC. Loss of this operational status message would indicate a failure of the AMM. Upon loss of 

the AMM status signal, the following should occur: 

1. By default, the SCA would be inhibited from accepting any new arrival or departure operations. 
18

2. ATC would be informed of an AMM failure though the loss of the periodic status message from 

the AMM. 

3. ATC should then restrict any new SCA entries and departures. 

4. The aircraft would identify the AMM failure through the loss of the AMM status message. 

5. The MFD would provide a notification to the pilot that the AMM has failed. 

6. Pilots with an assigned arrival sequence would use CTAF to corroborate their landing sequence. 

7. Each pilot would close his flight plan after landing, which is both a standard ATC normal 

procedure (ref. 9) and an HVO procedure. This would provide ATC a means for correlating the 

landing aircraft with the previously retained information that identified the current SCA traffic 

aircraft. 

8. At the completion of all HVO operations, the airport would revert to non-HVO operations. 

3.5.6 Loss of AMM Reception by a Single Aircraft 

As noted previously, the AMM would send a periodic operational status message to all proximate 

aircraft via the APDLC and to ATC. Loss of this operational status message could indicate an APDLC 

receiver failure on the SATS aircraft. Upon loss of the AMM status signal the following should occur: 

1. To confirm that the problem is single aircraft specific, the pilot of the aircraft without AMM 

reception would announce the loss of the AMM data via CTAF. If more than one aircraft has lost 

AMM reception, then the previous procedure (Loss of AMM Output) would be used. 

2. The pilots would use CTAF to corroborate their landing sequence. 

3. The aircraft would land in their original sequencing order. 

3.5.7 Loss of Voice Communications 

HVO procedures were developed for the situations when aircraft have lost their voice-radio 

communication capability. Following normal HVO procedures assures pilots of the ability to self separate 

within the SCA and land according to the AMM generated sequence. For aircraft in ATC airspace, 

traditional procedures (ref. 9) would be used in conjunction with the HVO arrival procedures. 

Arriving Aircraft Outside of the SCA: 

1. As noted previously, ATC would use traditional lost communication procedures. 

2. With the exception of the lost-communications aircraft, the AMM would inhibit all new 

operations and set the SCA status message to no-new-operations (NNO). 

3. The lost-communications aircraft would be provided with a normal, non-priority approach 

sequence via APDLC, assuming that all other entry constraints were met (Sec. 2.1). 
19

4. The lost-communications aircraft should descend to the altitude immediately above the SCA at a 

time appropriate for traditional lost-communications procedures. 

5. ATC would enable the AMM for new HVO operations after the lost communications aircraft has 

landed. 

6. The AMM would then resume normal operations. 

Arriving Aircraft Inside of the SCA:

If the aircraft had an approach sequence and subsequently lost its voice communications capability, 

normal operations would be continued. Voice-communication loss should not be a critical issue since the 

communication radio is only used as a secondary means for situation awareness and for redundancy in 

other off-nominal procedures. The communication radio should be required to initiate a SATS operation, 

i.e., it is part of the minimum equipment requirement. A loss of voice communications does mean a loss 

of the CTAF environment, so transitions to VFR follow existing procedures (ref. 8). 

Departing Aircraft:

 Aircraft that have lost their voice communication capability and are not airborne may not conduct an 

HVO departure. Airborne aircraft would use traditional IFR lost-communication procedures (ref. 9). 

3.6 Emergency Procedures 

3.6.1 Priority Landing Request from an Aircraft with an Approach Sequence 

This procedure would typically be used for an aircraft that is experiencing an emergency situation and 

must land immediately. This capability is valid only for aircraft that have an approach sequence assigned 

or are in a position where they would be eligible for an SCA entry notification (e.g., at the lowest 

available altitude over an SCA IAF). If they are not eligible for an SCA entry, they must coordinate with 

ATC since they are still under ATC control. Pilots within the SCA that have an emergency that precludes 

them from flying the complete instrument approach (engine or icing problems requiring an immediate 

landing) can still use the procedures in this section. Although terrain clearance cannot be assured in IMC 

when deviating from a certified approach (e.g., the pilot must proceed direct present position to the 

airport due to the emergency), the procedures below ensure all other pilots in the vicinity have awareness 

of the emergency and that the emergency aircraft has landing priority. 

Requesting Aircraft: 

For the aircraft requesting landing priority, the following procedure should be used: 

1. The pilot would announce the emergency and his intent over CTAF. 

2. The pilot would select the “emergency landing” feature on the MFD. 

3. The MFD would send the priority request to the AMM. 
20

4. The AMM would inhibit all new SCA operations and set the SCA status to NNO. 

5. The AMM would notify ATC that the SCA is in an inhibit status. 

6. The AMM would send the identity of the priority aircraft to all HVO aircraft. 

7. The MFD would inhibit all continuing-operations PA messages (e.g., open altitude, open 

approach) on the requesting aircraft. 

8. As soon as possible, the priority aircraft would begin the approach, procedurally spacing with 

respect to prior approach aircraft. If the approach spacing interval becomes too close, the pilot of 

the priority aircraft has the responsibility to request the preceding aircraft to perform a missed 

approach. Note that the requesting aircraft will not be assigned an approach sequence. If the 

aircraft was initially at the higher altitude at the IAF than the approach altitude, this aircraft 

would only begin a normal descent (e.g., 500 foot-per-minute descent rate) after crossing the IAF 

inbound on the approach. 

Other SCA Aircraft: 

1. The aircraft symbol on the MFD for the priority aircraft would be highlighted. 

2. Arriving aircraft that are already on the approach would continue with the approach procedure. If 

the emergency aircraft requests that the approach path needs to be immediately cleared for the 

emergency operation, these aircraft could execute an early missed-approach climb. 

3. If the priority aircraft was already on the approach or was the first aircraft in holding at an IAF 

(e.g., the next aircraft to initiate the approach), the AMM would not re-sequence the other 

aircraft. Otherwise, the AMM would re-sequence the aircraft waiting for an approach in their 

original order, excluding the priority aircraft. 

4. The AMM would send the new sequence information to all HVO aircraft. 

5. The MFD would notify the appropriate pilots of their re-sequence assignments. 

6. The MFD would inhibit all continuing-operations PA messages (e.g., open altitude, open 

approach) until the pilot of the re-sequenced aircraft acknowledged the re-sequence. 

7. The MFD would inhibit all approach-operations PA messages (e.g., open approach) until the 

priority aircraft has crossed the runway threshold. 

8. Once the priority aircraft has crossed the runway threshold, normal operations would be resumed. 

An example of this procedure is shown in figure 5. 

3.6.2 Priority Landing Request from a Departing Aircraft 

This procedure was designed to support a departing aircraft that is unable to continue the departure 

operation and must return for an instrument approach to the airport. 
21

Requesting Aircraft: 

Note that the first 7 steps of this procedure are the same as for Priority Landing Request from an 

Aircraft with an Approach Sequence. 

1. The pilot would announce the emergency and his intent over CTAF. 

2. The pilot would select the “emergency landing” feature on the MFD. 

3. The MFD would send the priority request via APDLC to the AMM. 

4. The AMM would inhibit all new SCA operations and would set the SCA status to 

no-new-operations (NNO). 

5. The AMM would notify ATC that the SCA is in an inhibit status. 

6. The AMM would send the identity of the priority aircraft to all HVO aircraft. 

7. The MFD would inhibit all continuing-operations PA messages (e.g., open altitude, open 

approach). 

8. As soon as possible, the priority aircraft would proceed to either IAF, at the lowest altitude, and 

begin the approach, procedurally spacing with respect to prior approach aircraft (if any). Note that 

this aircraft would not be assigned an approach sequence. If the approach spacing interval 

becomes too close, the pilot of the priority aircraft has the responsibility to request the proceeding 

aircraft to perform a missed approach. 

Other SCA Aircraft: 

1. The aircraft symbol on the MFD for the priority aircraft would be highlighted. 

2. Arriving aircraft that are already on the approach would continue with the approach procedure. If 

the emergency aircraft needs the approach path immediately cleared, the pilot of the emergency 

aircraft would request that the preceding aircraft execute an early missed-approach. 

3. Arrival aircraft that are holding at the IAF (i.e., not already on the approach) and are at the lowest 

altitude would be re-sequenced, if necessary, such that they would leave the IAF for the approach 

as soon as possible (i.e., the intent is to make a clear approach path for the emergency aircraft). 

These aircraft should make every attempt to expedite their approach operations. 

4. For arrival aircraft that are holding at the IAF (i.e., not already on the approach) and are not at the 

lowest altitude, the following should occur: 

- These aircraft would be re-sequenced, as required, for the approach. 

- If the aircraft has an approach sequence that has been changed (i.e., re-sequenced), the MFD 

would notify the SATS pilot to the changes in the approach information (e.g., new leading 

aircraft or MAHF). 
22

STANDBY 

Aircraft #2 

Aircraft #3 

Aircraft #1 

Aircraft 

requesting priority

- These aircraft would be given a STANDBY notification by the AMM. 

- The MFD would notify the appropriate pilots of their standby assignment. 

- The MFD would inhibit all continuing-operations PA messages (e.g., open altitude, open 

approach) until the pilot of the re-sequenced aircraft acknowledges the re-sequence. 

- The MFD would inhibit all continuing-operations PA messages (e.g., open altitude, open 

approach) until the emergency aircraft lands. 

5. Normal operations would be resumed once the priority aircraft has landed. 

An example of this procedure is shown in figures 7-10, with the chosen example portraying the worst 

approach sequencing situation prior to start of this procedure. The start of this procedure is shown in 

figure 7, with an aircraft on the approach and three other aircraft waiting to begin the approach. The 

approach sequence numbers are shown in this figure for these aircraft. 

Figure 8 portrays the situation immediately after the departing aircraft makes the priority request. At 

this point, the AMM would have re-sequenced and issued the new sequence numbers and, where 

appropriate, STANDBY notifications. Note that the action by the AMM has affected all of the holding 

aircraft. 

Figure 8. Example of a priority landing request from a departing aircraft: after re-sequence. 

Figure 7. Example of a priority landing request from a departing aircraft: initial situation.

Aircraft #3 

Aircraft #2 

Aircraft #4 

Aircraft #1 

Aircraft 

requesting priority
23

Figure 9 shows the situation as the second aircraft begins its approach. Note that the standard HVO 

airborne tools, using the AMM sequencing information, have provided the information to the second 

aircraft that it is safe to initiate its approach. Also note that the first aircraft has landed. 

Figure 9. Example of a priority landing request from a departing aircraft: aircraft #2 begins approach. 

Figure 10 shows the situation after the third aircraft begins its approach, again using its onboard tools 

to determine when to begin the approach. Figure 11 is a plan-view graphic of the situation shown in 

figure 10. 

Figure 10. Example of a priority landing request from a departing aircraft: aircraft #3 begins approach. 

Aircraft #2 

STANDBY 

Aircraft #3 Aircraft 

requesting priority

Aircraft #2 

STANDBY 

Aircraft #3 

Aircraft 

requesting priority
24

Figure 11. Plan-view of the situation of figure 10. 

Figure 12 shows the situation as the priority aircraft begins its approach. Note that while the standard 

HVO airborne tools have provided the information to the third aircraft to initiate its approach, the pilot of 

the priority aircraft, because of the emergency situation, will initiate the approach as soon as possible. 

Also note that if the approach spacing interval becomes too close, the pilot of the priority aircraft has the 

responsibility to request the proceeding aircraft to perform a missed approach. 

Figure 12. Example of a priority landing request from a departing aircraft: priority aircraft begins approach. 

Once the priority aircraft has landed, the STANDBY aircraft will be allowed to resume approach 

operations. Also note that all normal operations would be resumed once the priority aircraft has landed. 

4.0 Summary 

The ability to operate multiple small aircraft, in near all weather conditions, at virtually any small 

airport offers a unique opportunity for revolutionary transportation growth and passenger convenience. A 

previous paper (ref. 1) presented a concept for aircraft operating at airports where operations are currently 

restricted to the inefficiency of a “one-in/one-out” procedure. This new concept would allow for 

simultaneous operations by multiple aircraft in this non-radar “terminal” airspace around small nontowered airports. Aircraft operating in this airspace would need special avionics to participate that would 

Aircraft 

requesting priority
25

probably include near-term technologies, such as ADS-B and a communications data link, and 

appropriate self-separation tools. This concept would also require a new, relatively simple ground-based 

automation system, typically located at the airport, that would provide appropriate sequencing 

information to the arriving aircraft. 

The effort described in this paper expands the SATS HVO operational concept to include off-nominal 

situations that could be expected to occur in a future SATS environment. The situations that were 

examined were segregated into four categories: routine, such as a change of landing approach direction; 

procedural deviations, such as flying to the wrong MAHF; equipment malfunctions, such as a loss of an 

aircraft’s communication system; and emergency situations, such as a priority request for an emergency 

landing. SATS operational procedures were developed to accommodate these off-nominal situations and 

were described in this paper. Potential pilot and ATC workload issues were also considered in the 

development of these new procedures. With respect to potential problems relating to pilot workload, 

airborne display concepts were also defined to assist the pilot during these off-nominal situations. An 

effort was also made to minimize the impact on ATC following an off-nominal event in the SCA. 

Additionally, since both equipment requirements and equipment malfunctions are closely interrelated in 

off nominal situations, a candidate implementation scheme was also presented. 

In keeping with the SATS goal of achieving a realistic, operationally deployable system for the 2010 

timeframe, the development of these new operational procedures to support off-nominal situations again 

emphasized simplicity in the design. The development focus was on providing an operational concept 

that was safe, would enable more than one operation at a time, and would not require significant ground 

infrastructure costs or improvements. A significant design effort was also expended to minimize 

equipment requirements and changes to today’s operating rules. The operational concepts and procedures 

described in this paper were intended to be a starting point for additional designs and analyses. 

Operational concepts such as the one proposed in the fundamental SATS HVO concept documents and 

expanded here could enhance the opportunity for point-to-point air taxi or charter operations into smaller 

airports, providing greater convenience to the traveling public. 
26

5.0 References 

1. Abbott, Terence S.; Jones, Kenneth M.; Consiglio, Maria C.; Williams, Daniel M.; and Adams, Catherine 

A.: Small Aircraft Transportation System, Higher Volume Operations Concept: Normal Operations. 

NASA/TM-2004-213022, 2004. 

2. Conway, S.; and Consiglio, M.: A Method of Separation Assurance for Instrument Flight Procedures at 

Non-RADAR Airports, AIAA-2002-4448, August 2002. 

3. NASA Langley Research Center 2002: 2010 Concepts of Operations Document and Small Aircraft 

Transportation System: Systems Development and Evaluation Plan.

4. Jones, K.; Williams, D.; Consiglio, M.; Adams, C.; and Abbott, T.: IFR Operations at Non-Towered, 

Non-Radar Airports: Can We Do Better Than One-At-A-Time?, AIAA-2003-74, July 2003. 

5. Advisory Circular 23-1309-1C: Equipment, Systems, and Installations in Part 23 Airplanes. Staff of the 

Federal Aviation Administration, 1999. 

6. DO-259, Applications Descriptions for Initial Cockpit Display of Traffic Information (CDTI) Applications. 

RTCA, September 2000. 

7. Advisory Circular 120-70: Initial Air Carrier Operational Approval for Use of Digital Communication 

Systems. Staff of the Federal Aviation Administration, 2000. 

8. ARP 1402/4, Flight Deck Alerting System. SAE, July 1988. 

9. Aeronautical Information Manual: Official Guide to Basic Flight Information and ATC Procedures. Staff 

of the Federal Aviation Administration, 2005. 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Small Aircraft Transportation System, Higher Volume Operations 

Concept: Off-Nominal Operations

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Abbott, Terence S.; Consiglio, Maria C.; Baxley, Brian T.; 

Williams, Daniel M.; Adams, Catherine A.; and Conway, Sheila R.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

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National Aeronautics and Space Administration

Washington, DC 20546-0001

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L-19116

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NASA

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14. ABSTRACT

This document expands the Small Aircraft Transportation System, (SATS) Higher Volume Operations (HVO) concept to 

include off-nominal conditions. The general philosophy underlying the HVO concept is the establishment of a newly defined 

area of flight operations called a Self-Controlled Area (SCA). During periods of poor weather, a block of airspace would be 

established around designated non-towered, non-radar airports. Aircraft flying enroute to a SATS airport would be on a 

standard instrument flight rules flight clearance with Air Traffic Control providing separation services. Within the SCA, pilots 

would take responsibility for separation assurance between their aircraft and other similarly equipped aircraft. Previous work 

developed the procedures for normal HVO operations. This document provides details for off-nominal and emergency 

procedures for situations that could be expected to occur in a future SCA. 

15. SUBJECT TERMS

Aircraft operations; Aircraft systems; Approach spacing

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