Number 5 : March 1993
by Charles Drew
New solutions to old problems sometimes
result in a few new problems. Such is the case with Pre-Departure Clearances
(PDC's). Getting an IFR route clearance has often been difficult during busy
times at major airports, with pilots competing on a congested clearance delivery
frequency, and controllers having to read involved, often lengthy instructions.
With a pre-departure clearance, the
flight crew of a cooperating air carrier can get their IFR clearance from their
company rather than directly from an ATC facility. ATC still issues the clearance,
of course, but the transfer of information is directly to the air carrier's
dispatch department via teletype, computer link, or other method, rather than
by voice communication on an ATC frequency. The air carrier then provides the
clearance to the flight crew in the form of a printed message, or via ACARS.
But, there have been a few problems.
Don't Leave Home Without It
Some flight crews have departed without
an IFR route clearance:
- "After takeoff, I switched
to Departure Control as instructed. When I got no response I tried to verify
the frequency by retrieving the clearance from ACARS...When I saw there was
no PDC message stored I asked my First Officer for the correct frequency from
his verbal PDC and he said, eventually, 'Oh-oh, I forgot to get our clearance.'
" (ACN 198736)
And from another reporter:
- "Shortly after takeoff, ATC
told us to change transponder code. We complied, then checked pre-departure
clearance (PDC) for assigned squawk. Couldn't find paper, even though all
other paperwork was located. We either lost the PDC or never received it."
Wrong, Wrong, Wrong
Sometimes flight crews misread or
One variation of the PDC problem
is getting a PDC meant for another flight:
- "We receive our PDC's with
our flight packets containing release, weather, NOTAMS, and flight data sheet.
During review of the packet, I did not notice that our PDC did not match our
flight. After takeoff, Departure Control gave us a correction to our transponder
code. We corrected the code as requested and the PNF checked the code on the
PDC and showed it to me...I did not notice the wrong flight number, having
my...attention on flying...the Controller notified us that the code originally
used was for...flight XXX -- the PDC in our possession, but not our flight
YYY. The mix-up was verified and the flight continued without incident. The
mix-up was also not noticed by the other crew. Therefore, the error went undetected
by the original agent and four crew members." (ACN 192294)
Pilots of flights with multiple legs
face another potential problem:
- "Our flight (BOS-PWM) received
the wrong departure (PDC) clearance in BOS. It had the proper flight number
and date, but was the PDC for the ATL-BOS leg. When transponder code was reported
wrongly off the PDC, they only said, 'change squawk to read xxxx,' thus not
alerting the crew to the error. After takeoff, crew found out altitude cleared
to was wrong also, but did not violate any altitudes. Coordinated with...ATC,
company flight control and...operations to find error causes and correct."
It's even possible to get a PDC for
the correct flight number, but the wrong day:
- "I picked up our pre-departure
clearance at the counter in the terminal area about 15 minutes before departure...I
reviewed the clearance as I fought my way through the packed jetway to the
cockpit. As I entered my seat and began to review the departure and planned
route of flight, the APU shut down on its own. There was no external power
plugged in and no ground personnel in sight. I let the F/O continue cockpit
setup and went in to operations to get ground power hooked up and a mechanic
to look at the APU. When I got back to the cockpit, we ran the pre-departure
checklist, started engines, and taxied for takeoff. ...after takeoff when
Tower cleared us to Bay Departure Control with a turn to 030 degree heading,
we questioned which departure we were assigned. Tower impatiently informed
us we were on the San Francisco 6 which we then complied with. Later, reviewing
our pre-departure clearance, I found the problem was [that] the pre-departure
clearance I was given was for March/Sunday, not March/Monday...There's no
excuse for my missing the date on the pre-departure clearance, but I thought
this was another example of how a series of events can lead to a hazardous
situation." [Emphasis added.] (ACN 236984)
Changes Not Noted
Another of the problems noted in
PDC incidents is that flight crews fail to note changes on the PDC to their
filed or "usual" route:
- "Climbing out of SLC enroute
to LAX. ATC cleared us direct to FFU, flight plan route. After passing FFU
and proceeding on what we thought was our flight plan route, ATC asked us
what our routing was. We doubled checked our PDC and realized we had misread
the clearance." (ACN 218473)
Here is a problem where the flight
crew amended their route for operational considerations, but didn't catch the
fact that ATC apparently didn't have the requested change:
- "...The original aircraft
never left the hangar due to a mechanical problem. We were about an hour late
when maintenance switched planes. The new aircraft was not overwater equipped,
so the computer flight plan changed from overwater to an inland routing. Although
the aircraft had several items inoperative and an originating preflight [inspection]
had to be done, I felt we could still make the connecting complex at our destination
hub if we moved right along. The clearance came out of the aircraft printer.
It started out the same as filed and the route [was] loaded into the aircraft
[FMS]. What I failed to see was the clearance went out over the water down-line,
diverging from the filed inland route. We received direct clearance to a fix
past the point where the filed and the clearance route split. Approaching
our clearance limit, the next controller was unable to take us. We quickly
verified our filed routing with controller and were then cleared as filed.
During preflight I had thought the filed routing and the printed clearance
were the same because, at first glance, they looked identical. It's what a
fellow thinks he knows that hurts him." (ACN 235894)
Some reporters claim that the format
or structure of their printed or ACARS downloaded PDC has led to misinterpretations,
or to overlooking important amendments to their filed route. One Captain notes
the format problem following a track deviation after takeoff:
- "...as we inspected the pre-departure
clearance more carefully, we found that on or near the top [of the printed
PDC] was the filed route. Several lines down we found the [actual] clearance.
Because of other pressures on the crew at departure time, i.e., checklist
completion, ACARS entries, cockpit to ground crew communications, etc., there
was a tendency to give a higher priority to the top line of the pre-departure
clearance message than to lines farther down where the clearance routing is
located...We hope that the PDC can contribute to safety and smooth flow instead
of degrading them." (ACN 193587)
Even the physical printing of the
PDC can lead to problems:
- "The pre-departure clearance
(PDC) was received with the filed clearance on it and further down a change
of route...Received PDC late (at push time) and attached to another report
(final weather or weight and balance). The report had the ATC clearance printed
at the perforation in the paper. Just below was the filed clearance. Read
filed [route] vice ATC [clearance]." (ACN 207371)
- "...initial heading, altitude
and squawk are buried among other nonessential verbiage. Need better format
to highlight critical information since readback is no longer required."
In order to develop a better understanding
of the frequencies with which these events occur, we reviewed 42 reports that
described problems with PDC's. We also examined the consequences of PDC errors.
PDC Error Consequences
In 20 instances in 42 reports, a
track or heading error resulted from a PDC error, while an altitude deviation
was cited in 7 instances. There were 14 instances where the flight appeared
to depart without an IFR route clearance. Thirty-three of 42 reports provided
some evidence that a breakdown in cockpit coordination contributed to the incident.
Who Caught the Error
One of the factors we looked at was
whether the error was discovered before departure or after. In 37 of 42 incidents,
the PDC problem was discovered after departure. Perhaps this shouldn't be surprising,
in that errors discovered before departure may be considered non-incidents by
pilots and therefore unworthy of reporting to the ASRS.
A PDC error was more likely to be
caught by the controller (17 of 42 incidents) due to a route or altitude discrepancy
than for any other reason. The second most frequent means of error detection
was by the flight crew due to a transponder code discrepancy (11 of 42 reports).
Types of PDC Problems
Figure 1 shows the types of problems
and human errors experienced by flight crews in PDC incidents. Note that this
category allowed multiple responses to a single question, so there are more
citations (69) than reports (42) in the data set. The biggest problem appeared
to be failure on the part of the flight crew to adequately read the PDC, and/or
to note changes in the PDC.
In an effort to ensure that a flight
has received the proper IFR clearance, some facilities require the flight crew
to read back the PDC transponder code on Clearance or Ground frequency prior
to departure -- this can catch many potential PDC problems. Other ATC facilities,
however, do not use this verification procedure. In 17 of 18 instances in which
data was available, there was no transponder code verification procedure. Table
1 provides further detail.
1--Transponder Code Verification
|Transponder Code Verification
|Ambiguous, Not Stated, or Unknown
Many pilots are confused about the
"chain-of-responsibility" in the pre-departure clearance process.
Note the following ASRS report:
- "Forgot to get ATC route
clearance through ACARS...taxied out on Ground Control. No mention of lack
of clearance! Took off ...on Tower frequency. No mention of lack of clearance!
Switched to Departure Control. Again no mention of lack of clearance! They
told us to squawk yyyy as compared to zzzz. We did. That was our first clue
that something wasn't right. I checked our ACARS messages and found no ATC
PDC. Nothing was ever said to us one way or the other!" (ACN 205530)
It is important to remember that
ATC, having issued the PDC to the company, may or may not get an acknowledgment
of the company's receipt of the PDC. ATC certainly will not know if the flight
crew has received the PDC from company dispatch unless they (ATC) use some sort
of verification procedure.
Review of these PDC incident reports
leads to a number of suggestions for all parties involved in PDC transactions.
- Check for Clearance: PDC's
introduce a new variable in cockpit management -- how and when a clearance
is received. As one reporter notes, "...many airports do not have PDC's,
so it is not an acquired habit to check for a PDC..." (ACN 218886) Adding
an "ATC clearance received and reviewed" item to the written checklist
may help assist pilots' memory until the process is routine.
- Look for Errors: Is the
PDC for the right flight number? For the right trip segment? For the right
day and month? Scanning carefully for such errors may prevent an embarrassing
- Look for Changes: Are the
PDC and the filed route the same? Sometimes PDC formatting and presentation,
whether on ACARS or a printed sheet, can make detecting such changes difficult,
so it is important to review the PDC carefully.
- Practice CRM: Good cockpit
management and crew coordination techniques can help catch potential errors.
In the words of one reporter: "I have now selected a place in the cockpit
preparation flow where the PDC message (or radio delivered clearance) will
be reviewed by both pilots, and critical information set in proper windows
for departure." (ACN 194740) Are flight crew members in total agreement
on what the clearance is? If not, stop the flow and resolve the discrepancy.
- Query ATC: Getting a transponder
code change from ATC shortly after departure might be an indication that there
is a PDC clearance misunderstanding. If there is any question about the clearance,
ask your friendly controller for help.
- Reset The Transponder:
Resetting the transponder to 0000 (four zeros) after landing can help you,
or the next crew, detect lack of a PDC. Additionally, should a flight depart
without setting an appropriate IFR code on the transponder, ATC will be more
likely to quickly detect the problem. (Setting 1200 on the transponder may
lead a controller to believe the target is normal VFR traffic.)
Air Carrier Flight Departments
- Review PDC Format: Is the PDC
(whether using ACARS or a printed message) readable, clear, concise, and consistent,
or do flight crews need to look in different places to "piece together"
their clearance? Perhaps having the clearance displayed in a linear, cohesive
manner will reduce the opportunity for misinterpretation. It may be possible
to highlight changes to the filed route in bold type or in some other manner.
Similarly, placing the actual, full route clearance at or near the top of
the message could help.
- Provide PDC Training: It is recommended
that air carriers provide instruction to flight crews (during scheduled initial
and recurrent training sessions) in the use and interpretation of PDC's.
- Transponder Code Verification:
Use of clearance verification by requiring the flight to read the transponder
code appears to be effective where used. In the words of one pilot:
- "...one thing that might
be done to prevent departing without a PDC would be to standardize the way
PDC's are acknowledged, such as in ORD where you relay your assigned transponder
code to Clearance Delivery." (ACN 207872)
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