Narrative:

Air carrier X en route descent from 17000 ft to 11000 ft. ATC (ZME) issued a speed of 190 KTS. The clearance was issued without consideration if the flight crew would accept it, i.e., ATC expected this performance and adherence. Our altitude and speed respectively, were 14000 ft descending, 246 KTS. ATC manual 7110.65G paragraph 5-102 minima 'unless a pilot concurs in the use of a lower speed, use the following minima: a) to aircraft operating between FL280 and 10000 ft, a speed not less than 250 KTS or the....' during an ILS approach conducted in IMC, we were following a B757. ATC informed us that we were '4 mi in trail of preceding traffic, maintain 170 KTS to the marker...' because we encountered moderate chop at 4000 ft, we questioned ATC what type of aircraft we were following on the approach. Response, ' a B-757 at 4 mi.' our TCASII display was 3-1/2 - 3-3/4 mi. We immediately adjusted our flight path and speed to clear our position, although we continued the approach after the turbulence subsided. The tower along with approach control never advised us of the B-757. Never issued wake turbulence advisory or application. We did not know. Reference is 7110.65G paragraph 5-70, ie, 5 mi separation (5- 72(D)(2) and (F)(2)). Recently, the FAA administrator sent a letter to airmen regarding B-757 wake turbulence and ATC specific handling. In both cases noted above , ZME and bna approach control do not display proper application of the 7110.65G. Handbook and the letter to airmen.

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Original NASA ASRS Text

Title: ACR X ENCOUNTERED TURB ON APCH BEHIND B-757. POSSIBLE LTSS.

Narrative: ACR X ENRTE DSCNT FROM 17000 FT TO 11000 FT. ATC (ZME) ISSUED A SPD OF 190 KTS. THE CLRNC WAS ISSUED WITHOUT CONSIDERATION IF THE FLC WOULD ACCEPT IT, I.E., ATC EXPECTED THIS PERFORMANCE AND ADHERENCE. OUR ALT AND SPD RESPECTIVELY, WERE 14000 FT DSNDING, 246 KTS. ATC MANUAL 7110.65G PARAGRAPH 5-102 MINIMA 'UNLESS A PLT CONCURS IN THE USE OF A LOWER SPD, USE THE FOLLOWING MINIMA: A) TO ACFT OPERATING BTWN FL280 AND 10000 FT, A SPD NOT LESS THAN 250 KTS OR THE....' DURING AN ILS APCH CONDUCTED IN IMC, WE WERE FOLLOWING A B757. ATC INFORMED US THAT WE WERE '4 MI IN TRAIL OF PRECEDING TFC, MAINTAIN 170 KTS TO THE MARKER...' BECAUSE WE ENCOUNTERED MODERATE CHOP AT 4000 FT, WE QUESTIONED ATC WHAT TYPE OF ACFT WE WERE FOLLOWING ON THE APCH. RESPONSE, ' A B-757 AT 4 MI.' OUR TCASII DISPLAY WAS 3-1/2 - 3-3/4 MI. WE IMMEDIATELY ADJUSTED OUR FLT PATH AND SPD TO CLR OUR POS, ALTHOUGH WE CONTINUED THE APCH AFTER THE TURB SUBSIDED. THE TWR ALONG WITH APCH CTL NEVER ADVISED US OF THE B-757. NEVER ISSUED WAKE TURB ADVISORY OR APPLICATION. WE DID NOT KNOW. REF IS 7110.65G PARAGRAPH 5-70, IE, 5 MI SEPARATION (5- 72(D)(2) AND (F)(2)). RECENTLY, THE FAA ADMINISTRATOR SENT A LETTER TO AIRMEN REGARDING B-757 WAKE TURB AND ATC SPECIFIC HANDLING. IN BOTH CASES NOTED ABOVE , ZME AND BNA APCH CTL DO NOT DISPLAY PROPER APPLICATION OF THE 7110.65G. HANDBOOK AND THE LETTER TO AIRMEN.

Data retrieved from NASA's ASRS site as of July 2007 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.