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Probe into 737 near-overrun details temperature blunders

November 21, 2018 / DAVID KAMINSKI-MORROW

As the crew programmed the flight-management computer prior to departure, a figure of minus 47°C was erroneously entered as the outside air temperature.The flight-management computer uses outside air temperature to calculate the N1 level for engine thrust.Such an abnormally low temperature figure would cause the N1 calculation to be “significantly below” that required for take-off thrust, says the Air Accidents Investigation Branch.It points out that minus 47°C was the outside air temperature for the first waypoint after top-of-climb, recorded on the pilot’s log.Neither pilot noticed the error,” it adds. The crew then exacerbated the situation by entering a correctly-calculated assumed temperature of 47°C, which reduced the thrust requirement further.