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Subject of Alert No. of Alerts
Aircraft or aircraft equipment 8
Airport facility or procedure 11
Chart, publication, or nav database 1
TOTAL 20
In 1990, the Pre-Departure Clearance (PDC) program
was introduced at a number of U.S. airports. This system
allows pilots to obtain IFR clearances through aircraft
ACARS (Aircraft Communication Addressing and Reporting
System) display units prior to taxi. The program has
reduced the volume of voice communications and related
use of the Clearance Delivery frequency.
Not long after the launch of the PDC program, ASRS began
receiving related incident reports. ASRS Directline first
published an analysis of PDC issues in March 1993 (Issue
#5). This analysis noted that confusing PDC formats were
one of the leading problems reported. In almost half of the
PDC incidents reviewed, a track or heading error resulted.
In December 1996, ASRS reviewed PDC incident reports to
be included in the first ASRS Operational Issues Bulletin.
Inconsistent PDC formats were again identified as a
significant user issue. Both the Directline article and the
Operational Issues Bulletin are available on the ASRS web
site (http://asrs.arc.nasa.gov/publications/), under “Safety
Publications.”
Increase this past year in PDC-related reporting prompted
ASRS to revisit PDC issues. A recent review of 71 relevant
incident reports confirmed that a concern we first identified
16 years ago—PDC formats—is a recurrent problem for
many pilots. Specifically, our recent review identified the
following PDC format issues:
• Listing of both filed and cleared routes
• Unclear or ambiguous routing formats
• Unnecessary route revisions (amendments)
Listing of Both Filed and Cleared Routes
When pilots view a PDC on the ACARS CDU (Control
Display Unit), current industry practice is to include the
original filed route along with the ATC-cleared route on
the PDC “page.” For many pilots, the visual and mental
tasks of sorting out which routing to fly are confusing.
An air carrier Captain described how confusing the
appearance of both a filed and cleared routing can be:
n When calling ATC for a clearance via radio, and if
cleared as filed, the controller states ‘cleared as filed.’
In contrast, PDC seems to present a jumbled mess of
information. If “Cleared as Filed’ was typed, then the
pilot could simply refer to their release. If not cleared
as filed, then the route should be shown on PDC and
that would be a cue to the pilot that something is
different compared to what is on the release. Instead,
the filed route is shown on the PDC, sometimes [shown]
completely, sometimes ‘truncated....’
Other ASRS reporters weighed in with similar
observations and advice:
n One solution would be to only display the actual ATC
clearance vs. showing both the filed and the change, or
use plain English stating ‘Change route to read.’...As long
as two routings are printed on the PDC, the filed and the
amended routing, someone will fly the wrong one.
n ...Have only the cleared routing show up in the PDC
message...so there is less of a chance that a crew flies the
unrevised route.
n It seems counter-productive to continue to put the
original route on the PDC page. By putting only the
[cleared] route, there is not a‘ two-route’ choice...
After many years of operational experience with PDC’s,
most air carriers require that PDC’s be printed and
reviewed by both pilots prior to programming the
navigation system. This procedure provides redundancy
and ensures that both pilots agree on the cleared route.
In some cases, however, cockpit ACARS units may lack
printers, and in these instances it is customary for the
First Officer to copy the PDC from the screen, then brief
the Captain prior to takeoff. This procedure is problematic
for two reasons: it assumes the First Officer will copy
the PDC correctly, and it also assumes the briefing of the
Captain will be accurate.
A report filed by the Captain of a high-performance jet
illustrates how an error chain can develop when the First
Officer is solely responsible for route verification:
n Received clearance via PDC. PDC listed both filed route
and cleared route. The Second In Command copied the
filed route...Upon departure, Controller sent us direct to a
fix that was not on our ‘clearance.’ A quick question cleared
up the confusion...
A procedural safety net for reviewing PDC’s on screen was
proposed by another reporter:
　
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