speed protection modes b737
hello air america & others,
to follow on on alexban, i would say: use the proven "kiss"(keep it simple st*pid") principle & think basic flying : if you where the autopilot, how would you handle/correct the situation?
basically you have overspeed/placard(gear & flap) protection & underspeed protection . an additional performance reversion mode exist for placard speed & minimum speed.
1) if all the gimmicks: autopilot/flightdirector & autothrottle are engaged & all is functioning normally, you will have full speed/reversion mode protection :
- assume level flight for simplicity, if tending to fly to fast, the autothrottles(a/t) will reduce thrust & keep slightly below limit speed.
- same , if too slow, a/t will increase thrust & keep slightly above min speed.
a speed >15kt must be selected to remove the underspeed symbol in the mcp window.
- let's climb, we now have an additional protection : min speed reversion mode: if asking an excessive performance in vertical climb speed(v/s), when reaching a limiting minimum indicated airspeed & a/t condition: autopilot reverts to level change & controls pitch with attitude.
if then a minimum performance level (v/s), cannot be maintained without decelerating, the a/p disconnects & it is up to you to take over control.
2) in your example, autothrottle disengaged, you still have limited speed protection.
- vmo/mmo protection : yes(a/p goes in level change).
- placard protection for gear & flap : no.
- performance reversion mode for min speed : no. so in this case you can stall the aeroplane when in alt hold or glide slope capture,(please, don't).
as a gop(good operating practice) : if flying on automatics : use a/p + f/d + a/t, if flying manually, use hotas : hands on throttle & stick except for take off & climb, where you can use auto throttle (cfr mr boeing recommendation).
for info, speed window on mcp(mode control panel), will flash in above modes preceeded by overspeed(filled 8 symbol)/underspeed(capital A symbol).
a last remark & i hope many will agree, the interphase man(or woman)/machine & logic of the boeing automatics are not so difficult to master & understand, but the accuracy of keeping selected parameters by the autopilot would definitely need some additional engineering, to keep it mild.
hope this helps,
kind regards,
bm