Does anyone know why on NG's Boeing have altered the white bug to set at
V2 +15 for departure and Vref +20 for approach? This softwear change appeared with no explanation and no-one in our outfit knows why
My guess is because the FCTM advises that in event of engine failure on final approach (737-800/900) and it is decided to continue approach and sufficient thrust is not available for landing flaps, speed should be increased to 20 knots over the previously set flaps 30 or 40 Vref. This is equal to at least VREF for flaps 15. Hence white bug at Vref + 20.
On other 737 versions, including the Classics and -600 and -700 under similar scenario, the speed is increased to +15 knots above previously set flaps 30 or 40 VREF and this policy is reflected by setting a white bug at VREF +15. That said, the FCTM advice for the 737-400 situation is that too should have the speed increased to +20 knots