Autopilot Puzzles

[ORTAC22]

May I enquire what parameters are involved which dictate the moment,after take-off,at which it is safe/prudent to engage the Autopilot.
Many thanks.

[Duchess_Driver]

Depends on many factors.... Mostly guidance will be given in the company SOP's - which can of course be deviated from in the event of an emergency.

The cynic in me would have answered 'The Accountants' - as typically the Autopilot/Flight Management Computer flies it much more efficiently than manual operation!

[parabellum]

On the Boeing aircraft I have flown 400' climbing out, usually noise abatement procedure related.

[RAT 5]

what parameters are involved after take-off to decide when it is safe/prudent to engage the Autopilot.

The 400' RA is a technical limitation on B737.
First; the autopilot is a tool to relieve the pilot from having to control the a/c manually and allow them to have a better overview of the whole operation. When do you feel that is necessary? Each to their own and in each scenario; differing everyday.

Safe:
All systems affecting the A/P are working correctly.
A/C in trim and established on correct profile. Not good to engage and allow the A/P to sort out any out of trim condition.
PF/PM are fully aware of the 'what is going on'.
After selected to engage it is VITAL to ensure it really is engaged in both channels and then monitor it for correct performance. Remember it is to help you operate the a/c not take over command. Various crashes occurred because there A/P as not engaged and the pilots failed to realise it.

Prudent:
Busy airspace for the departure, especially low level SID cap.
Challenging weather.
Perhaps night, bright stars & moon can lead to some strange illusions climbing steeply.
PF is tired on a return sector.
Anything that causes hi-workload below FL100.

No fast rules. Each can make up their own guidelines.

[Denti]

Normal to low workload i usually wait until we have accelerated to cruise climb speed, around FL120 or so. High workload, tired, bored or just not in the mood i put him on as low as 100ft off the ground. Most colleagues fly manually to between 100ft and several thousand feet, usually until the initial turns are fun. Flying along a straight line is pretty boring and otto can easily take care of that. Used to be 400ft lowest back on the boeing for technical reasons.

[ORTAC22]

Most informative-thanks to all.

[seen_the_box]

On the Airbus (320 family and I assume the rest of the FBW aircraft too), the technical limitation is 100' or 5 seconds after liftoff.

We don't really have a company limitation; you can hand-fly as much as you want. The flight directors must be on for take off here though, so I tend to engage the autopilot pretty quickly after takeoff. I don't find following a flight director particularly rewarding!

Approaches are a different matter; those, we can fly however we like. Raw data, manual thrust: anything goes.

[Piltdown Man]

Every (public transport) aircraft has a minimum use height for the autopilot. These heights depend on the mode (eg, climb, 'cruise', approach) and possible other factors. Fokker 70/100 aircraft can use theirs from 35' in the climb down to zero feet on certain approaches. And as stated above, 400' in the climb is a common limit for other aircraft. The reason for this specific value is probably because nobody can be really be bothered to certify for lower heights. Also, 400' is often the lowest acceleration level in common usage.

PM

[AeroSpark]

I know that a lot of aircraft can land fully automatically, even holding the rwy centreline on roll out. What stops an autopliot being able to take off automatically?

[RAT 5]

Nothing, but it's not necessary. An autoland can only be conducted on an suitable ILS runway. That is how the suitable a/c can track the centreline; not all a/c can do that; not all runways are suitable ILS equipped. The reason for autolands is that the landing is more important than takeoff. Weather can not always be as expected at destination and landing is not an option; take off is. Autoland is a benefit to maintaining schedules. It is a simper procedure to automate than takeoff. There is not real benefit in designing/certifying/training/maintaining an auto-takeoff capability.