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Altitude change


Bert Pieke

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Pardon me if this is described somewhere, but I am not sure how I do an altitude change.

If I am established, with ALT hold, at an altitude, and dial in the new altitude, what

do I do (in detail) to get the airplane to climb or descend to the selected altitude?

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Pardon me if this is described somewhere, but I am not sure how I do an altitude change.

If I am established, with ALT hold, at an altitude, and dial in the new altitude, what

do I do (in detail) to get the airplane to climb or descend to the selected altitude?

Hi Bert,

The AP in the Twin Otter is very rudimentary in terms of functionality. The altitude hold function holds a current altitude. The altitude you set in the window is actually just for an alert, and not something the AP is based to. So, for changing altitude, you only have two options. You can disengage the ALT hold, and descend manually, or, you can select IAS mode and reduce or increase your power, depending on if you want to climb or descend. IAS hols works in a similar fashion in that it will hold the current indicated airspeed that it was engaged at.

So, if you are at 5000' and wish to descend to 3000' and hold your current airspeed, say 135kts, then select 3000' in the window to give you an alert, then click the 'IAS' button to engage the IAS hold. Now, reduce your power by 10 or so pounds of torque to begin your descent. The IAS hold will trim the aircraft to keep maintaining that airspeed. Upon reaching 3000', press the 'ALT' button to reactivate altitude holding, and you should be good to go!

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Now that sounds very rudimentary indeed, and does not match what I am seeing..

The aircraft will actually level off at the selected altitude, if I direct it there, so your

explanation does not quite match what the aircraft does, sorry :confused2_s:

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Comprehensively explained in the manual, Bert.

The a/p itself does exactly as Kyle is saying. Nothing more, nothing less.

What you are seeing is the interaction between the a/p and th FD-112V Flight Director which DOES have a pitch-command function and auto-levelling capability.

So, from your scenario described:

Disengage vertical hold mode on the a/p (disco the `Alt`), then press the FD button ALT ALERT. Also dial in the new alt on the indicator.

From there simply adjust pitch trim on the yoke to attain the desired rate of climb or descent and the aircraft will level itself at the new altitude, extinguishing the ALT ALERT light and re-engaging the `ALT` on the a/p.

Clear?

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