Narrative:

On the ILS to runway 04 in lga (in VMC conditions); we were sequenced behind a B757. Initially we were vectored off the localizer to give adequate separation between us and the B757. Once we were back on the localizer and flying at our assigned speed of 180 KTS; we appeared to be 4 miles behind the B757. Once we were handed off to lga tower; the controller asked if we had the B757 in sight. I replied that we did not; and then asked why we needed to. The controller ignored my question. When the B757 was over the numbers; the controller again asked if we had him in sight. I replied that we did. He then asked us to maintain visual separation with the traffic; and that we were cleared to land. The landing was normal. Suggestions; I filed this report to bring attention to what I believe is an unsafe ATC practice. I called and spoke to one of the tower controllers after landing. I suspected; and he confirmed; that we were asked to maintain visual separation with the preceding aircraft to absolve the tower controller of separation responsibility; since it appeared to him that we were getting closer than the required 4 miles behind the B757. Had we not offered to do so; he would have commanded a go-around. The tower controller acted correctly; and used proper procedure. The problem in this case is that the separation with the B757 is for wake turbulence. If a flight crew accepts visual separation; they then may inadvertently waive the wake turbulence separation without realizing it. ATC is not required to mention this fact in this particular situation. When taking off behind a B757; or a heavy aircraft; ATC must provide proper separation. The flight crew may waive the separation; but ATC is not allowed to even ask them to do so; the request must be initiated by the crew. Why is this only a requirement for taking off behind a heavy aircraft; and not when landing behind one? If the requirements can't be the same; then at the very least; ATC should be required to make the crew aware that they are in fact waiving wake separation when they accept visual separation by asking the question: 'will you waive your wake separation?'- or something similar. Hitting wake turbulence at slow speed close to the ground is extremely dangerous. I don't think ATC should be allowed to reduce wake separation on an aircraft without making it explicitly clear that they are doing so.

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Original NASA ASRS Text

Title: Air carrier pilot described a minimal wake separation event on short final to LGA when ATC requested the flight crew to maintain visual separation; the reporter suggesting current ATC wake separation applications are unsafe.

Narrative: On the ILS to Runway 04 in LGA (in VMC conditions); we were sequenced behind a B757. Initially we were vectored off the localizer to give adequate separation between us and the B757. Once we were back on the localizer and flying at our assigned speed of 180 KTS; we appeared to be 4 miles behind the B757. Once we were handed off to LGA Tower; the Controller asked if we had the B757 in sight. I replied that we did not; and then asked why we needed to. The Controller ignored my question. When the B757 was over the numbers; the Controller again asked if we had him in sight. I replied that we did. He then asked us to maintain visual separation with the traffic; and that we were cleared to land. The landing was normal. Suggestions; I filed this report to bring attention to what I believe is an unsafe ATC practice. I called and spoke to one of the Tower Controllers after landing. I suspected; and he confirmed; that we were asked to maintain visual separation with the preceding aircraft to absolve the Tower Controller of separation responsibility; since it appeared to him that we were getting closer than the required 4 miles behind the B757. Had we not offered to do so; he would have commanded a go-around. The Tower Controller acted correctly; and used proper procedure. The problem in this case is that the separation with the B757 is for wake turbulence. If a flight crew accepts visual separation; they then may inadvertently waive the wake turbulence separation without realizing it. ATC is not required to mention this fact in this particular situation. When taking off behind a B757; or a heavy aircraft; ATC must provide proper separation. The flight crew may waive the separation; but ATC is not allowed to even ask them to do so; the request must be initiated by the crew. Why is this only a requirement for taking off behind a heavy aircraft; and not when landing behind one? If the requirements can't be the same; then at the very least; ATC should be required to make the crew aware that they are in fact waiving wake separation when they accept visual separation by asking the question: 'Will you waive your wake separation?'- Or something similar. Hitting wake turbulence at slow speed close to the ground is extremely dangerous. I don't think ATC should be allowed to reduce wake separation on an aircraft without making it explicitly clear that they are doing so.

Data retrieved from NASA's ASRS site as of April 2012 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.