Autopilot activation

[forthbridge]

Hi Guys

Just a quick 'real world' question.....

How much of a 'lag' is there in real life when switching to AP? I ask as I've been eyeballing a few long xposures of A/C taking off at night, and a fair few of the light trails 'step' that is, there's the initial climb angle, then a 'flat' followed by another climb. The 'step' must only be for a split second or two but is noticeable.

Curiously (but not surprisingly) it's just like looking at a flight altitide graph...

[ianhind]

Jim

Which airport?

At many airports there is a required initial steep climb angle and then a reduced rate of climb often for "noise abatement". I wonder if what you are seeing is a throttling back at the end of the initial climb so that the subsequent reduced climb rate does not result in exceeding the speed limit with the same power setting?

Just my 2p worth.

Ian

[forthbridge]

HI Ian

Edinburgh... and believe it or not I can't find the shots in question now!

[DispatchDragon]

Sounds very much like a noise abatement procedure -- in fact what yo described is what I used to watch on the 1-11s departing Luton many years ago -- level off reduce power to noise abatement then when speed is stabilsed climb again.

Leif

[forthbridge]

Cheers Guys

thinking about it, it may be a little low for engaging AP. When and if I find the shots again, I'll link to them

[Chris Trott]

In addition, depending on the flap schedule, just retracting the flaps can cause that "step" to appear as the aircraft looses lift from the flaps and then regains it as the aircraft accelerates from the reduction in drag.

[petermcleland]

The Trident SOP was to engage the AP at 500 feet, but I don't know what they do in today's aircraft. Naturally, if it was "your leg" then you might choose to hand fly some way into the climb, but to hand fly in the cruise was frowned upon. You might also choose to hand fly the descent if the weather at destination was expected to be fine :flying:

[Nigel H-J]

but to hand fly in the cruise was frowned upon

I appreciate that by flying on auto-pilot leaves the crew free to concentrate on other things (apart from crosswords and girlie mags) but.....why was it frowned upon?

Regards
nigel.

[petermcleland]

Because hand flying a Trident at altitude required such keen concentration to maintain a tight Flight Level and Course and would mean that other things would tend get neglected...Much safer to engage the AP and engage the Height Lock to remove any risk of a "Level Bust". Many, probably most, would retain the heading locked to the heading knob on the compass, rather than a "Beam or Radial Display" on the HSI. They would then constantly monitor drift and adjust the heading allowance by twiddling the knob. This would allow a very relaxed ability to select and switch nav aid frequencies and displays etc. to keep the aircraft going where it was supposed to.

It is a different story on the descent as he would have already tuned the necessary nav aids and would be free from the concentration of maintaining a flight level or altitude. Many pilots liked to fly the descent manually...I often did, but actually preferred to manipulate the AP to control my descent.

[Nigel H-J]

Thanks Peter.

Regards
Nigel.