FAR Part 25 Second Stage Climb with Turboprops.

[Panama Jack]

I am looking through FAR Part 25 to solve a friendly dispute with a fellow pilot.

The FAR Part 25 turboprop aircraft has Auto Feather, however, I would like to know whether the second stage climb is predicated on an engine being feathered or not. The debate is whether, in the event of a non-feather, the dead engine should be feathered as soon as practicable or whether one should wait until after level off height.

FAR 25.111(4) only gives the following hint:

4) Except for gear retraction and propeller feathering, the airplane configuration may not be changed, and no change in power or thrust that requires action by the pilot may be made, until the airplane is 400 feet above the takeoff surface.

The big question is whether the performance will be available to meet second segment climb without feathering, based on the weights in our Performance book.

Anybody?

[Tinstaafl]

My understanding is that feathering is required.

Using the paragraph you quoted, you wouldn't expect the climb to be done with the gear out, would you? Same logic for feathering.

Even more importantly, if the flight path is constructed based on autofeather operating then if autofeather fails to operate for any reason you no longer meet a performance condition around which terrain separation is based.

[Panama Jack]

My same thinking. Anybody have any idea on where I can cite this?

[Mad (Flt) Scientist]

Ac25-7A chg1 (p87) in addressing the requirememnts of 25.111(c)(4) - Configuration Changes - specifically states:

(iii) Drag reduction for a manually feathered propellor is permitted for flight path calculations only after reaching 400ft above the takeoff surface

Therefore if the propellor is NOT feathered AND auto-feather was taken credit for during the performance calculations you will not meet the assumptions of the takeoff flight path calculation.

Because the auto-feather system is thereby rendered quite important (!) another paragraph (241) in the same AC deals with the criteria for an auto-feather system. In particular, the 25.1309 requirements must be met for a 10^-9 failure rate, as failure is deemed to be catastrophic, in combination with an engine failure. Autofeather itself must be 10^-4 or better.

In certification terms you should *never* be presented with the case where an engine fails and auto-feather does no operate. If it does and you get stuck in that <10^-9 case then you probably should think about manually feathering, but chances are you're having a bad day already....

[Panama Jack]

That is quite interesting.

Previously, I flew this same aircraft for an airline and a very experienced operator of the type, and there was a plethora of possible procedures that we had, including, V1 cuts for Prop Auto-Feathers, and Prop Negative Feather.

The current company I work for (a corporation) has relatively basic procedures compared to my previous employer, and only has the V1 cut, prop autofeathers procedure. In my current flying takeoff briefings I state that we will complete an immediate engine shut down, even below 400 feet, if the prop does not feather.

Interestingly, at my previous employer, the two conditions for shutdown below 400 feet were 1) Engine negative feather and 2) Engine fire. What are your thoughts on the Engine fire?

[john_tullamarine]

The other concern which must be highlighted is that the Design Standards are dynamic, living documents.

Just because one reads whatever in FAR 25 at current issue, please do not fall into the trap of thinking that your faithful, old dogwhistle (certificated to an ancient version of the Standard) has any knowledge of the the current words. One ALWAYS MUST dig out the TCDS for the Type, check the frozen applicable Standard ... and then USE THAT version of the Standard in bar room discussions ....

[Old Smokey]

Certification requirements definately require feathering of the propeller, whether it be manually or by auto-feather.

In a piston engined aircraft you might get away with waiting for 400 feet before feathering, if you were at very light weights.

Any engine which drives a propeller must produce sufficient power to meet it's own internal requirements, and the balance available supplied to the propeller. If the engine fails, the propeller now extracts from the airstream that power required to meet the engines internal requirements.

A piston engine requires about 10% of the power produced to meet it's internal requirements, a turbine engine requires about 2/3 of the power produced for 'itself', leaving 1/3 for the propeller.

If we consider a 1000 HP piston engine failed, the propeller will extract about 100 HP from the airstream. A 2 engined aircraft could probably maintain level flight, and a possible reduced climb.

If we consider a 1000 HP turbine engine failed, the propeller will extract about 2000 HP from the airstream. A 2 engined aircraft would be incapable of further flight (except downwards).

It is for this reason that many turbo-props have medium and high propeller stops, to hold the propeller at a high, low drag angle in the event of windmilling. These stops would invariably not be reached during takeoff, only later in the climb or cruise regime.