Narrative:

Over the past couple months there have been numerous air carrier flights that have flown a route different than expected. Denver center to date has 14 documented events. Conversations concerning this indicate that this has occurred many more times that did not get formally documented. Each instance that has been reviewed traces the apparent cause to a route amendment that was part of an automated pre-departure clearance (pre departure clearance). In each case; flight crews stated that the amended route was missed due to the obscure reference to amendments in the pre departure clearance format. It is apparent that this problem is not carrier or route specific. The common thread is that a portion of the filed route was amended in the pre departure clearance and that amendment was not flown. The following is an excerpt from a pilot report (used with permission) which is typical for these events: 'after programming the FMC; we failed to properly identify an ATC routing change upon receiving pre departure clearance. Original cleared routing: -kden BAYLR2 hbu dvc***klax-. ATC routing change; -BAYLR2 tehru dvc-. With ATC routing change listed directly above the original cleared routing on the pre departure clearance; we inadvertently verified the cleared routing as the routing change. On departure at top of climb at bobba intersection we proceeded to fly the hbu transition. Shortly after turning den ATC cleared us direct to tehru flight planned route. ATC then questioned us about the clearance we received. At that time we believed the hbu transition to be correct. ATC then gave us a frequency change. We then reviewed the pre departure clearance and all that [occurred] up to the deviation and concluded that we mis-identified the routing change. Several controllers later; we were advised to call den ATC about possible route deviation. I called immediately after completing the flight. The ATC supervisor indicated to me that this same deviation has been happening on a regular basis and that my explanation is the same as on most such occurrences. The ATC routing change and the original cleared routing being so close together allows for the potential to make this mistake repeatedly. We realize the error and will be more diligent to not repeat this error.reporter's suggestions for Change1. The pre departure clearance should reflect only the changed routing and omit the part of the original [filed] route that was changed. We would then be able to compare [the cleared route] with the filed flight plan. We inadvertently compared the route directly below the ATC changed routing with original flight plan.2. Require flights to verify with clearance delivery the SID and transition which would mitigate airborne deviations. Other airports do this. Examples: lax and lga.3. If route deviations are a regular occurrence on a particular route as indicated to me by den ATC supervisor; then communication between ATC and airlines to change flight plans so that ATC doesn't need to change the cleared routing needs to take place.4. Ultimately; I need to do a better job with pre departure clearance verification to not allow this to happen again'end of excerptit appears that the formatting for pre departure clearance messages may be such that amended routes are being overlooked. Pilots have told me that the formatting is not consistent between airports making it easy to miss pertinent parts of the clearance. Perhaps the formatting can be standardized and amended routes can be highlighted with inverse text. It is our belief that we are only capturing a fraction of the total occurrences of this type event and that is probably occurring throughout the NAS. These events cause significant risk as aircraft are making unexpected turns which have in some cases placed them in unsafe proximity to other traffic.

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Original NASA ASRS Text

Title: An ARTCC controller and a B737 Captain addressed PDC formatting issues that may have been critical factor in numerous reported similar events.

Narrative: Over the past couple months there have been numerous air carrier flights that have flown a route different than expected. Denver Center to date has 14 documented events. Conversations concerning this indicate that this has occurred many more times that did not get formally documented. Each instance that has been reviewed traces the apparent cause to a route amendment that was part of an automated Pre-Departure Clearance (PDC). In each case; flight crews stated that the amended route was missed due to the obscure reference to amendments in the PDC format. It is apparent that this problem is not carrier or route specific. The common thread is that a portion of the filed route was amended in the PDC and that amendment was not flown. The following is an excerpt from a pilot report (used with permission) which is typical for these events: 'After programming the FMC; we failed to properly identify an ATC routing change upon receiving PDC. Original cleared routing: -KDEN BAYLR2 HBU DVC***KLAX-. ATC routing change; -BAYLR2 TEHRU DVC-. With ATC routing change listed directly above the original cleared routing on the PDC; we inadvertently verified the cleared routing as the routing change. On departure at top of climb at BOBBA intersection we proceeded to fly the HBU transition. Shortly after turning DEN ATC cleared us direct to TEHRU flight planned route. ATC then questioned us about the clearance we received. At that time we believed The HBU transition to be correct. ATC then gave us a frequency change. We then reviewed the PDC and all that [occurred] up to the deviation and concluded that we mis-identified the routing change. Several controllers later; we were advised to call DEN ATC about possible route deviation. I called immediately after completing the flight. The ATC Supervisor indicated to me that this same deviation has been happening on a regular basis and that my explanation is the same as on most such occurrences. The ATC routing change and the original cleared routing being so close together allows for the potential to make this mistake repeatedly. We realize the error and will be more diligent to not repeat this error.Reporter's Suggestions for Change1. The PDC should reflect only the changed routing and omit the part of the original [filed] route that was changed. We would then be able to compare [the cleared route] with the filed flight plan. We inadvertently compared the route directly below the ATC changed routing with original flight plan.2. Require flights to verify with clearance delivery the SID and Transition which would mitigate airborne deviations. Other airports do this. Examples: LAX and LGA.3. If route deviations are a regular occurrence on a particular route as indicated to me by DEN ATC Supervisor; then communication between ATC and airlines to change flight plans so that ATC doesn't need to change the cleared routing needs to take place.4. Ultimately; I need to do a better job with PDC verification to not allow this to happen again'END OF EXCERPTIt appears that the formatting for PDC messages may be such that amended routes are being overlooked. Pilots have told me that the formatting is not consistent between airports making it easy to miss pertinent parts of the clearance. Perhaps the formatting can be standardized and amended routes can be highlighted with inverse text. It is our belief that we are only capturing a fraction of the total occurrences of this type event and that is probably occurring throughout the NAS. These events cause significant risk as aircraft are making unexpected turns which have in some cases placed them in unsafe proximity to other traffic.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.