King Air F90 A/P

[PicMas]

Having just started training on the King Air F90 I am trying to learn the systems. The autopilot has two functions: IAS - I suppose this function sets a pitch to maintain a constant IAS - Is that correct?

The other is "IAS PRF" - Any good explanations on that one?

Did look over the training manual without success (don´t have the original with the supplement)

Why do you not T/O and land with the yawdamper ON? Is it the logic reason that nosewheel steering is affected by the same actuator moving the rudder?

regards

[PicMas]

Is it really true that NOBODY has a suggestion for the function of the "IAS PRF" function?!?

[LGW Vulture]

Maybe the wrong forum, you might try the Bizjets / GA forum instead.

[IHL]

I fly a C90 with a collins 65 auto-pilot. It has the following vertical modes: ALT (ALT HOLD) ALT SEL (Altitude preselect) VS (VERTICAL SPEED) & IAS (airspeed hold) & GA (Go-around) it does not have IAS PRF.

In IAS it will hold the airspeed. It can be adjusted by mometarily (1/4 sec) tapping the vertical control rocker switch; each tap is equivalent to a change in airspeed of 1 knot (up or down).

In VS one tap on the rocker switch is = to 200 FPM.

In ALT one tap is = to a 25FT altitude change.

Holding the switch longer than 1/4 sec changes the pitch at a rate of 1 degree per second.

I have no idea what IAS PRF means .

[CorpoRat]

Having the yaw damper off in the event of an engine failure will allow the pilot greater control. The yaw damper does not know your engine has failed. 5deg into live, 1/2 ball out.

[Chippie Chappie]

I must stress that this is a guess as I don't fly the Kingair but on other Collins systems (i.e. APS-85), there is a "Performance Select" function and this is what PRF may stand for. The function maintains a constant, pre-determined airspeed, such as "Normal climb" and there may be other speeds programmed in such as a "High" and "Low Speed" climb.
Hope this helps,
Chips

[His dudeness]

Been flying the F90 only once. That one was equipped with an early romian empire radio stack and very basic A/P.
However I guess Cippie Chappie has got it right. The 65 Collins on a B200 has a "climb" function that basically keeps 160 KIAS up to FL100 and reduces speed by 2 kts/1000ft down to 125 KIAS, which is the recommended cruise climb schedule.

[IHL]

I foregot to mention the YAW damper. If you ever forget to shut off the YAW damper after you've done the auto-pilot check you will quickly realize why it is off for take off and landing. The rudder pedals are very very stiff to move, control would be difficult-not impossible- just difficult.

The other point the YAW damper has nothing to do with the nose wheel steering they are 2 completely different independent systems.

[BB954]

PicMas

I used to fly a 1981 King-Air B200 fitted with King Gold Crown avionics. It had a button on the auto-pilot controller marked "Spd Prf" the function of which was to steadily reduce the IAS as the aircraft climbed to cruise altitude/flight level. Trouble was it didn't work very well and I gave up using it prefering to control the climb speed manually with the pitch control rocker switch. Hope this may help.

[PicMas]

I want to thank you all very much for taking the time to reply.

I was of course wrong about the "IAS PRF" and am glad for the correction, it was "SPD PRF".

It's all starting to make sense now.