ASRS Directline

 Issue Number 5 : March 1993

PDC's... the problems with Pre-Departure Clearances

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. Solution: PDC's.

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:

And from another reporter:

Wrong, Wrong, Wrong

Sometimes flight crews misread or misinterpret PDC's.

Wrong Flight

One variation of the PDC problem is getting a PDC meant for another flight:

Wrong Leg

Pilots of flights with multiple legs face another potential problem:

Wrong Day

It's even possible to get a PDC for the correct flight number, but the wrong day:

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:

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:

Confusing Format

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:

Even the physical printing of the PDC can lead to problems:

And finally:

ASRS Analysis

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.

Figure 1 PDC Problems

Transponder Verification

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.

Table 1--Transponder Code Verification

Transponder Code Verification Used 1
Transponder Code Verification NOT Used 17
Ambiguous, Not Stated, or Unknown 24
Total Reports 42

Many pilots are confused about the "chain-of-responsibility" in the pre-departure clearance process. Note the following ASRS report:

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.


  1. 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.

  2. 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 incident.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  1. 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.

  2. 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.

FAA/ATC Facilities

  1. 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:

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