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Federal AviationAdministration
The Human Element in Actual Communication Performance (ACP)
Presented to: PBCS Workshop
By: Kim Cardosi, [email protected]
Date: 17-19 June 2015
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The Human Element in Actual Communication Performance (ACP)
• What is it?
• How do we measure it?
• What affects it?
• What can be done to protect against known errors?
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Data Link Performance Monitoring• The ICAO Global Plan calls for the implementation of a
performance based system and ICAO Annex 11 requires that data link system performance is monitored to verify that an acceptable level of safety continues to be met.
• The Performance-based Communication and Surveillance Manual (Doc 9869) provides guidance material on the required data points and how to calculate the actual communication performance (ACP), actual communication technical performance (ACTP), pilot operational response time (PORT). – This guidance was formerly contained in Global Operational Data
Link Document (GOLD)
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ACP
Up Down
Sent) (UplinkReceived) (WILCOACP Required Communication Monitored Performance (RCMP)
∆Down
2∆UpACTP Required Communication
Technical Performance (RCTP)
ACTPACPPORT RCP Pilot Operational Response Time (PORT)
1 Uplink Sent Date/time ATSU sent CPDLC clearance to the aircraft2 MAS Received Date/time ATSU receives the MAS for the CPDLC clearance3 WILCO Sent Date/time aircraft sends WILCO response for the CPDLC clearance4 WILCO Received Date/time ATSU receives WILCO response for the CPDLC clearance
1 42 3
The measurements (in seconds) are calculated as follows:
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Factors influencing ACP
• Equipment– Some indications of an ATC message are more efficient at
attracting attention than others.
– Time required to access the message depends on the flight deck interface.
• Airline procedures/training – Speed/accuracy tradeoff
• Clearances – and combination of clearances– Pilots respond faster and more accurately to some clearances
compared to others.
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ZNY Sample of ACP - Specification: RCP 240 95% benchmark
January 1, 2013 to June 30, 2013 (6 months) - 3 most common messagesMessage Count ACP <=180 sec ACTP <=120 sec PORT <=60 sec
CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level)U26 U129 11,231 99.2% 99.6% 96.5%
CLIMB TO (level); REPORT MAINTAINING (level)U20 U129 8,801 99.2% 99.7% 97.3%
MAINTAIN (speed)U106 1,902 99.2% 99.5% 98.5%
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PORT Varies By Message Type (1 of 2) Message Count PORT < 60 sec
CLIMB TO (level); REPORT MAINTAINING (level)U20 U129 8,801 97.3%
REPORT MAINTAINING (level); CLIMB TO (level)U129 U20 706 97.5%
REPORT MAINTAINING (level); CLIMB TO REACH (level) BY (time)U129 U26 860 96.1%
CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level); Due to Traffic
U26 U129 U166 732 94.0%
Due to Traffic; MAINTAIN (level); AT (time) CLIMB TO (level); CLIMB TO REACH (level) BY (time); MAINTAIN (speed) OR LESSU166 U19 U21 U26 U129 109 83.5%
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PORT Varies By Message Type (2 of 2)
Message Count PORT < 60 sec
CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level)U26 U129 11,231 96.5%
CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level); WHEN CAN YOU ACCEPT (level)
U26 U129 U148 220 69.1%
CLIMB TO (level); REPORT MAINTAINING (level)U20 U129 8,801 97.3%
CLIMB TO (level); REPORT MAINTAINING (level);WHEN CAN YOU ACCEPT (level)
U20 U129 U148 181 68.5%
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What’s known about pilot error?
• Few studies on the nature of pilot error associated with data link based on operational data.
• Data entry errors are to be expected.
• Conditional clearances have long been regarded as problematic.
Federal AviationAdministrationFAA Study on
Conditional Clearances
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What is a conditional clearance?• A vertical clearance that includes a restriction, such as
– a time or place for starting the climb or descent– a time or place for when the level is to be reached
Ref Conditional clearance message elementMessage element with “AT” restriction
UM21 AT [time] CLIMB TO [level] or AT [time] CLIMB TO AND MAINTAIN [altitude]UM22 AT [position] CLIMB TO [level] or AT [position] CLIMB TO AND MAINTAIN [altitude]UM24 AT [time] DESCEND TO [level] or AT [time] DESCEND TO AND MAINTAIN [altitude]UM25 AT [position] DESCEND TO [level] or AT [position] DESCEND TO AND MAINTAIN [altitude]
Message element with “BY” restrictionUM26 CLIMB TO REACH [level] BY [time]UM27 CLIMB TO REACH [level] BY [position]UM28 DESCEND TO REACH [level] BY [time]UM29 DESCEND TO REACH [level] BY [position]
Note.— Message elements shown in bold text indicate the preferred choice, per Doc 4444, and should be used for new implementations. The second choice is shown in italic text and indicates legacy implementations (e.g. most FANS 1/A aircraft) that are considered acceptable (GOLD, Appendix A).
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Conditional Clearances – identified issues
– “AT TIME/POSITION…” – pilots can miss the condition and act immediately or forget to comply when condition is met.
• Most often act immediately – especially when clearance follows a request for a climb
– CLIMB/DESCEND to level BY TIME/POSITION –has been misunderstood (relatively few cases)
• BY – misinterpreted as by way of, or initiation (as opposed to completion) of maneuver
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Doc 4444 Appendix 5 – Proposed Changes
Current Doc 4444 Proposed 2016
Ref Message element Message element
Message element with restriction for starting a climb or descent
UM21 AT [time] CLIMB TO [level] AT TIME [time] CLIMB TO [level]
UM24 AT [time] DESCEND TO [level] AT TIME [time] DESCEND TO [level]
Message element with restriction for when a level is to be reached
UM26 CLIMB TO REACH [level] BY [time]CLIMB TO REACH [level single] BEFORE TIME [time]
UM27 CLIMB TO REACH [level] BY [position]
CLIMB TO REACH [level single] BEFORE PASSING [position]
UM28 DESCEND TO REACH [level] BY [time]
DESCEND TO REACH [level single] BEFORE TIME [time]
UM29 DESCEND TO REACH [level] BY [position]
DESCEND TO REACH [level single] BEFORE PASSING [position]
Per RTCA SC-214 / EUROCAE WG-78
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Use of conditional clearances
• KZWY – 20-25% of operational communication are conditional clearances
• In comparison, about 5 times more than KZAK; more than 10 times more than PAZA
KZWY KZAK PAZA2010 2011 2012 2010 2011 2012 2010 2011 2012
% DL CCs of all DL Transactions 23.1% 21.1% 19.1% 2.9% 3.1% 3.1% 1.4% 2.2% 1.8%
% V CCs of all V Transactions 26.7% 25.2% 23.8% 5.0% 5.3% 6.0% 1.2% 1.4% 1.3%
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Conditional Clearance LHDs
• Large height deviations (LHDs) in which the restriction in a conditional clearance was a causal factor
• Focus – New York– Data are more readily available
– Conditional clearance LHDs can be correlated to the NAT vertical risk
• Evaluated data mostly for the period 2009 to 2012– Estimated error rates for conditional clearance LHDs
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KZWY conditional clearance LHDs
• Message use –“BYs” 10 times more common than “ATs”
• CC LHDs – The “ATs” (UM2126) dominate
0
4
8
12
16
20
UM
2126
UM
2428
UM
2429
UM
21
UM
26
UM
27
UM
28
UM
29
CC-AT CC-BY
CC
LH
D C
NT
V-CC LHD CNT - KZWY WATRSV-CC LHD CNT - KZWY NATDL-CC LHD CNT - KZWY WATRSDL-CC LHD CNT - KZWY NAT
020406080
100120
UM
2126
UM
2428
UM
2429
UM
21
UM
26
UM
27
UM
28
UM
29
CC-AT CC-BYC
C L
HD
TA
WL
(min
utes
)
V-CC LHD TAWL - KZWY WATRSV-CC LHD TAWL - KZWY NATDL-CC LHD TAWL - KZWY WATRSDL-CC LHD TAWL - KZWY NAT
New York (KZWY) CNT - 35 New York (KZWY) TAWL - 200 minutes
By message type
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KZWY conditional clearance LHDs
• Increasing trend in conditional clearance LHDs associated with UM2126; decrease with UM26
0
1
2
3
4
5
6
7
8
9
2009 2010 2011 2012 2009 2010 2011 2012
CC-AT CC-BY
CC
LH
D C
NT
V-UM29
V-UM28
V-UM26
DL-UM29
DL-UM28
DL-UM26
V-UM2429
V-UM2428
V-UM2126
DL-UM21
DL-UM2126
0
10
20
30
40
50
60
2009 2010 2011 2012 2009 2010 2011 2012
CC-AT CC-BY
CC
LH
D T
AW
L (m
inut
es)
V-UM29
V-UM28
V-UM26
DL-UM29
DL-UM28
DL-UM26
V-UM2429
V-UM2428
V-UM2126
DL-UM21
DL-UM2126
New York (KZWY) CNT - 35 New York (KZWY) TAWL - 200 minutes
By message type and by year
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Error rate forconditional clearance LHDs
Message type
CPDLC (DL)
Voice (V)
Message type
CPDLC (DL)
Voice (V)
CC-AT 16 4 UM2126 22 3.4
CC-BY 0.7 0.3 UM26 w/o UM21 0.6 0.2
0.
5.
10
15
20
25
2009 to 2012
Erro
r rat
e(b
y m
sg ty
pe)
(per
10,
000
msg
s)
KZWY DL Total CC-AT
V Total CC-AT
DL UM2126
V UM2126
DL Total CC-BY
V Total CC-BY
DL UM26 w/o UM21
V UM26 w/o UM21
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Contributory factors –what we learned
• Fewer cases of forgetting to comply with AT than expected; few cases missing BY
• Errors involving ‘native English’ carriers as prevalent as non-native English carriers
• Aircraft type/display type not a factor in errors associated with UM2126 LHDs
• ATC seldom issues CLR with the AT restriction; ATC issues CLR with the BY restriction 10 times more (which sets pilot expectation)
• Flight crew misses AT restriction, regardless of whether or not it is in response to a flight crew request or negotiation
• UM26 overshadows UM21; BY is the compelling factor
• PORT for UM 21+ UM 26 (U19 U21 U26 U129) - 90.5% of PORT < 60 indicates that its unlikely that GOLD procedure was followed.
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Recommendations (1 of 4)
• Aircraft manufacturers and equipment suppliers should consider avionics functionality that alerts the flight crew for conditional clearances containing the AT restriction when:
– It is time for the flight crew to execute the maneuver after meeting a condition; or
– The flight crew is executing a maneuver and the condition has not been met.
– Is being implemented in some modern aircraft.
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Recommendations (2 of 4)
• Standardize controller procedures: (see GOLD)
– Order of message elements should be standardized (predictable)
– Use of multi-element messages – only messages that are dependent should be sent in the same message; WHEN CAN YOU ACCEPT (level) should be sent separately
– In response to requests or following level negotiations (e.g., response should issue same level as requested; conditional clearances should be preceded by UNABLE)
– Use of ADS-C reports to determine the level of aircraft; this eliminates the need to request level reports as part of a conditional clearance in ADS-C environments
– Minimize use of “dual restriction” conditional clearances, e.g., UM2126
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Recommendations (3 of 4)
• Flight crew procedures– Each crewmember should silently and individually
read each CPDLC message and then confer, whenever feasible, and at a minimum, before execution of a control instruction.
– Printers, when available, should not be used as the primary means of reading the CPDLC clearance. Printed CPDLC clearances must be verified against the primary display before use.
– This information is in the GOLD manual (Doc 10037).
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Recommendations (4 of 4)
• Language proficiency training for pilots that use data link should include the ability to read and write Aviation English.
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