B757 Flight Crew notices VMO pointer at an abnormally low position (270 knots) during climbout and elects to return to departure airport.
Synopsis
B757 Flight Crew notices VMO pointer at an abnormally low position (270 knots) during climbout and elects to return to departure airport.
Narrative
Start; taxi; takeoff were normal. Climbing through approx 12;000 FT; I noticed the VMO/MMO pointer remaining stagnant at approximately 270 KTS. As we climbed it was obvious that we would get an overspeed warning if the climb was continued. I requested a level off and slowed to 250 KTS. I contacted Dispatch and Maintenance to discuss the problem and a decision was reached to return. The remainder of the instruments seemed normal and since I was not sure what had caused the anomaly; we elected to return immediately. Landing weight was checked on final at 210;000 LBS and an uneventful landing was accomplished. After shutdown; a Maintenance Supervisor advised us that the VMO/MMO switch was in the incorrect aux position rather than normal position. Although the position of the switch is not accessible by aircrew both the First Officer and I failed to note that the mach pointer was lower than normal during preflight. The pointer is not acutely lower than normal in this condition and in nearly 14 years on this airplane I have never seen this before. Although I checked the indicator I just did not notice the low mach pointer. I will certainly in the future pay particularly close attention to this detail.
Second reporter narrative
Climbing through approx 12000' Captain noticed that VMO/MMO pointer remained stagnant at approximately 270 knots. As we climbed it was obvious that we would get an overspeed warning if the climb was continued. Captain requested a level off and slowed to 250 knots. Captain contacted Dispatch and Maintenance to discuss the problem and a decision was reached to return. The remainder of the instruments seemed normal and since we were not sure what had caused the anomaly; we elected to return. After shutdown; a Maintenance Supervisor advised us that the VMO/MMO switch was in the incorrect aux position rather than normal position. Although the position of the switch is not accessible by aircrew I failed to note that the MACH pointer was lower than normal during preflight. The pointer is not acutely lower than normal in this condition and being new to the aircraft (4 months) I failed to catch the problem.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.