Narrative:

A B757 was cleared by ZLA to deviate left of course when able proceed direct ekr. The B757 was northbound on the left deviation and decided that he needed to deviate to the right; he made about a 90 to 110 degree right turn to go right around some weather. I informed him that a right turn when he was cleared to deviate left was a pilot deviation; any right turn should have taken the aircraft direct to ekr. He said that because he was cleared to deviate left of course that gave him approval to make any deviations necessary as long as he remained left of his previous flight plan. Two other air carriers earlier in the day did similar turns opposite the direction they were cleared to deviate. I am curious if other countries allow aircraft to deviate as they please as long as the stay to the left/right of the aircraft's previous route. On occasion I have cleared an aircraft to deviate up to i.e. 10 miles left or right of their filed route; but I am very clear on my expectations. If an aircraft is cleared to deviate left of course when able direct to a fix; their new route is a direct line from the deviation to the cleared fix; as a result any turn right of that line would require a clearance from ATC. I believe this is a huge safety issue; I don't know if the pilots are so caught up in getting around the weather that they forget what their clearance was or if they think it is no big deal and just work their way around the weather. As a controller when I issue a left deviation I do not separate aircraft to the right of aircraft unless the on course turn could become a factor. Pilots making these types of deviations potentially put themselves and other aircraft in the NAS at a huge collision risk. I believe that the airlines need to educate their pilots so that they are clear on what is expected from them.

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Original NASA ASRS Text

Title: ZLC Controller voiced concern regarding the interpretation of a 'weather deviation clearance' and what turn limitations are in fact authorized from ATC's perspective.

Narrative: A B757 was cleared by ZLA to deviate left of course when able proceed direct EKR. The B757 was northbound on the left deviation and decided that he needed to deviate to the right; he made about a 90 to 110 degree right turn to go right around some weather. I informed him that a right turn when he was cleared to deviate left was a pilot deviation; any right turn should have taken the aircraft direct to EKR. He said that because he was cleared to deviate left of course that gave him approval to make any deviations necessary as long as he remained left of his previous flight plan. Two other Air Carriers earlier in the day did similar turns opposite the direction they were cleared to deviate. I am curious if other countries allow aircraft to deviate as they please as long as the stay to the left/right of the aircraft's previous route. On occasion I have cleared an aircraft to deviate up to i.e. 10 miles left or right of their filed route; but I am very clear on my expectations. If an aircraft is cleared to deviate left of course when able direct to a fix; their new route is a direct line from the deviation to the cleared fix; as a result any turn right of that line would require a clearance from ATC. I believe this is a huge safety issue; I don't know if the pilots are so caught up in getting around the weather that they forget what their clearance was or if they think it is no big deal and just work their way around the weather. As a controller when I issue a left deviation I do not separate aircraft to the right of aircraft unless the on course turn could become a factor. Pilots making these types of deviations potentially put themselves and other aircraft in the NAS at a huge collision risk. I believe that the airlines need to educate their pilots so that they are clear on what is expected from them.

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.