ASRS Operational Issues Bulletin 96-01
December 20, 1996

Confusion in Using Pre-Departure Clearances

 

Background

In 1990, the FAA implemented the Pre-Departure Clearance (PDC) program at a number of U.S. airports. This system allows pilots to obtain IFR clearances through aircraft ACARS units prior to taxi-out, thus eliminating the need for verbal communication on Clearance Delivery frequencies. The program's objective of reducing congestion on Clearance Delivery frequencies has been met. However, a number of ASRS incident reports indicate that pilots and controllers frequently experience confusion in using the PDC system.

In order to further investigate the causes of PDC-related problems, a team of ASRS analysts reviewed a relevant selection of incoming ASRS incident reports, and conducted interviews with aviation professionals at Oakland Center, San Francisco Tower, several major air carriers, NASA, and FAA Headquarters in Washington, D.C. This operational bulletin will focus on the two most frequently cited areas of concern: (1) inconsistent PDC formats, and (2) lack of confirmation procedures for PDC receipt.

Inconsistent PDC Formats

Revised Routings. The PDC problem most frequently reported to ASRS is confusing depiction of clearance revisions or amendments. Most PDC revisions are depicted by dashes before and after the revision. The original filed clearance is printed on a separate line immediately following the revised clearance. However, many flight crews apparently are not trained to observe the formatting differences between clearance revisions and filed clearances. As a result, flight crews often believe that revisions are erroneous (or separate clearances), and revert to their original filed clearances. A recent report from a flight crew illustrates:

The type of confusion experienced by this flight crew over their PDC routing is potentially hazardous, as noted by a controller reporter to ASRS:

"It has been my experience...that several times per shift aircraft which have received PDCs with amended routings, have not picked up the amendment...I have myself on numerous occasions had to have those aircraft make some very big turns to achieve separation." (ACN # 233622)

The sources consulted by ASRS suggested several potential solutions to this problem:

Assigned SIDs. Another source of confusion occurs when assigned Standard Instrument Departures (SID) information is placed outside the routing section of the PDC. An ASRS report explains:

This pilot and other ASRS reporters had a single recommendation for how to handle SID information in PDCs:

Lack of Confirmation Procedures For PDC Receipt

Another frequently reported problem is flight crews' forgetting to obtain PDCs, and taking off without a clearance. This oversight occurs primarily at airports that do not have a confirmation procedure for PDC receipt by the flight crew. The first clue that the PDC has been forgotten usually is when the Departure controller gives the crew a transponder code and Departure frequency, as described by these ASRS reporters:

ASRS sources had several suggestions for combatting the "forgotten PDC" problem:


Sample PDC Formats

An ASRS analyst team obtained samples of actual PDC formats used by air carriers. Excerpts from several of these clearances are depicted on pages 1-3. Following each clearance is an explanation of the formatting inconsistency identified by ASRS.

SAMPLE 1

##DPTR CLRNC##
FLT 1234-05 SEA - SFO
XAL1234 SEA
T/B73J/G P2150 RQ330
XPDR 3572 EDCT 2200
SEATTLE2 RV J70
ELMAA
MAINT 9000 EXPT REQ
ALT 15NM AFT T/O
CONTACT DPTR CTL ON
120.4
CLNC VOID 15 MIN
AFTER EDCT
SEA ELMAA5 CVO
J589./. SFO

Problem: This PDC cites two departures, SEATTLE2 and ELMAA5. The flight crew must sort out which departure to use.

 


 

SAMPLE 2

_HX PDC MESSAGE
PDC 25 XAL1234 2602 PHX
/B72S/G P1616 455 200
--DRK6 DRK J92 BLD--
PHX DRK6 DRK J92./. SFO
EDCT 1818

Problem: There is no apparent difference between the revision

--DRK 6 J92 BLD--

and the filed clearance. This is potentially confusing to a flight crew.

 


 

SAMPLE 3

_EA PDC MESSAGE
PDC 10 XAL1234 3516 SEA
T/B72S/G P1455 872 330
--ELMAA5 CVO--
SEA J70 ELMAA J589./.
EDCT
ELMAA5.CVO DEPARTURE

Problem: The revision is between dashes:

--ELMAA5 CVO--.

ELMAA (the same routing) is repeated on the next line for no apparent reason.

 


 

SAMPLE 4

A recent letter to ASRS from an air carrier pilot noted another type of PDC discrepancy. This pilot is involved with daily flights from Los Angeles and San Francisco to Vancouver (CYVR), British Columbia. The final flight segment is SEA DRCT PAE DRCT ACORD ACORD6 CYVR. The PDC duplicates the filed flight plan up to Seattle, but then truncates the rest of the clearance as shown:

PDC 173 FLT XAL1234/12
KSFO
T/DC9/A P2110 BQ350
XPRD 1720 EDCT 1310
--SF06 SFO RBL--
KSFO RBL J65
SEA***CYVR

Problem: Because of the truncated PDC routing, the flight crew must call Clearance Delivery before takeoff to verify the actual route after SEA. The discrepancy between the filed and PDC routes creates confusion for the flight crew. The need to call Clearance Delivery also nullifies the advantage of using a PDC.


Summary of PDC Recommendations


Users Note

The information presented in this bulletin is subject to some of the known limitations of ASRS data: (1) reported incidents cannot be independently verified; (2) reporters to ASRS may have a variety of reporting motivations and biases; (3) the voluntary nature of ASRS report submissions makes it impossible to accurately assess the full population of events for a given incident type. In spite of these limitations, ASRS report processing analysts have a unique vantage point in monitoring aviation system issues and problems from the incoming report flow of approximately 2,600 reports each month.