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Speed for low speed and shutdown


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Might be due:

1- Sudden and large cut of fuel during the low speed selection, with a speed more than 30 knots (high ram air interring the engine) may cause the engine to flame out.

2- Shutting-down the engine with a speed more than 20 knots is putting the engine under a higher than normal negative torque (unnecessary stress on the safety coupling).

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Engine shutdown should not be accomplished when taxi speed, wind velocity, or a combination of wind velocity and taxi speed is greater than 20 knots. Engine shutdown under these conditions may damage the safety coupling. When doubt exists as to the effective speed, the shutdown should be delayed.

Ref. TO 1C-130H-1 (Flight Manual) (Date of Issue 1 August 2002) (Section 2 page 91).

For the reason behind the low speed selection limit, I couldn't find any reference yet.

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I agree you will not find the 20 knot speed in the maintenance pubs...

The reason is in system operation...

(The following is stated in several different places)

The NTS system is inoperative with blade angles in the ground range, inoperative as in cammed out so the feather valve is not actuated in a negitive torque condition. Thus all negitive torque is transmitted to the safety coupling.

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Thanks a lot tenten...it is great have information inside your FM.From my FM382C-57D just state

Low speed ground idle operation

"Prior to downshifthing from normal to low speed ground idle, ensure that forward velocity including wind is less than 30 knots"

Normal engine shutdown

"When is is necessary to shutdown engines during taxi, ensure that forward velocity including wind is less than 20 knots"

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We are using FM 382C-14E for military registered aircrafts and OM 282G-65C for a civil registered aircraft; And in both they do have the two cautions (word for word as you stated in your post); But also in both they did not state the technical reason behind the limits. The one that I sent as a reference which may solve 50% of your question is not in used for our aircrafts.

The fact that most of the books dealing with the operators/maintainers with the words DO and DONT without giving the reason behind is unavoidable; thus sometimes making life hard to find out.


I agree 110% of the technical reason that you bring our attentions to, on the fact that “NTS†is mechanically deactivated during Ground Range (cammed-out) in which the safety coupling during normal ground shutdown is not backed-up by that system, but this fact will not satisfy the question of brother apexlined; he is looking for a direct authorized technical reference concerning the effect of aircraft velocity on the shutting down or the low speed selection. In another words he is looking for the velocity effect factor.

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I would imagine that the military manual is more up-to-date than my copy of the Allison Operating Manual which states:


Operating Manual

Allison Engine Company

MODELS 501-022, and -022A

Before moving the lew-speed ground idle' switch from LOW to NORMAL or NORMAL to LOW, observe the following precautions:

(1) Discontinue use of compressor bleed air from the first engine to be shifted.

(2) Set power at or as near minimum torque as practicable (between 9° and 30° power lever position).

(3) Reduce forward velocity to normal taxi speed (less than 5O knots).

Press low-speed ground idle switch if taxiing at low-speed condition is desired.

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