AS350 FADEC Manual Mode Operation
 

In another thread, the notion was floated that a pilot could NOT takeoff in an AS350B3/2B helicopter with the governor in the MANUAL mode. Supposed underlying reasons included doubting the airworthiness of the aircraft, contradiction to the RFM, violation of MEL and/or unsafe operation. So I did some checking. But first, the backstory:

1. The AS350B3/2B aircraft has a single channel FADEC which automatically controls the engine throughout the flight envelope. In the event of a FADEC failure, the pilot is alerted via illumination of a red “GOV” caution light. In this event, the fuel flow is frozen at the current rate, and the pilot must manipulate a twist grip throttle to properly control the rotor RPM until landing. While the prescribed emergency procedure doesn’t state a landing urgency, the description implies performing a landing as soon as PRACTICABLE.

2. The AS350B3/2B cockpit FADEC controls include an AUTO/MANUAL selector switch, for the sole purpose of simulating a complete FADEC failure. With the MANUAL mode selected, the red “GOV” caution light is illuminated and the FADEC no longer controls fuel flow (control must be accomplished manually by the pilot).

What does the RFM Say?

AFAIK, the AS350B3/2B RFM provides no limitation against flight with the FADEC mode selector in the MANUAL mode. However, the absence of any limitation(s) does seem odd, especially given that the RFM specifically prohibits switching the engine selector to idle in-flight. The RFM also prohibits reducing the twist grip in-flight except for autorotational training, as required by emergency procedures and during test flights. Yet its mute about any MANUAL mode limitations.

What does the FAR say?

FAR §91.7 Civil aircraft airworthiness states,

(a) No person may operate a civil aircraft unless it is in an airworthy condition.

(b) The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur.

The excepted definition of “airworthy” involves a two-pronged test:

(1) conforms to its type certificate (as modified by supplemental type certificates and by Airworthiness Directives); and

(2) a condition for safe operation.

I doubt anyone would consider a fully functioning AS350B3/2B with it’s mode selector in the MANUAL position as not conforming to its type certificate. Afterall, the aircraft was granted its type certificate with the switch, and the switch is operable. Furthermore, the thought that it is not safe for operation in this mode implies it also wouldn’t be safe in-flight in the MANUAL mode either. FAR 91.7 states, “no person may operate…” which doesn’t differentiate between takeoff, cruise or landing. Furthermore, the manufacturer provides procedures for flight in the MANUAL mode (see below), so obviously they don’t believe its unsafe.

What does the MEL say?

A Minimum Equipment List (MEL) provides for release of an aircraft with inoperative equipment. But the MEL does not contain obvious required equipment such as rotor blades, engine, or a FADEC. Under MEL use, these obvious items must be operative at all times. Accordingly, an inoperative system and/or component is one that malfunctions to the extent that it does not accomplish its intended purpose and/or is not consistently functioning normally within its approved operating limit(s) and/or tolerance(s). It follows that switching an instrument or piece of equipment OFF, or into an alternative mode of operation doesn’t meet the definition of “inoperative.” And if one couldn’t fly with an item turned off, wouldn’t that likewise lead to the rational that hand flying an instrument approach when an autopilot was installed should be prohibited also?

What does the manufacturer say?

Eurocopter (now Airbus Helicopters) published a Service Letter (No. 1702-71-05, dated 4/12/06), entitled “Ecureuil AS350 B3 and AS550 C3 helicopters Different versions of twist grip and FADEC controls.” This letter provides technical information on the operation of the engine governor and controls as well as training and flight procedures with the engine in the governor back-up mode. While the letter doesn’t prescribe particular maneuvers to be performed for manual governor training, it does directly address in-flight and landing procedures.

It should be noted that the Service Letter highlights that training for total governor failure must be carried out with an experienced instructor.

What does the FAA say?

While not directly involving the AS350, the FAA has published a Special Airworthiness Information Bulletin regarding a Bell Helicopter Textron Model 407 helicopter configured with a similar type FADEC engine control (SW 05-70). The SAIB specifically addresses handling procedures for FADEC transitions from automatic to manual mode in the B-407 aircraft. The SAIB makes the following training recommendations for the B-407:

“Ground training should be followed by a takeoff/hover/traffic pattern and landing in manual mode, which will allow you to become familiar with the required manipulation of the throttle and controls. Once you are comfortable with flight in manual mode, simulated FADEC failure emergency procedures can be carried out in flight.”


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Does anyone still think its not allowable?

Nothing I've read thus far suggests to me it's allowable in the AS350B3 to take off with a FADEC that does not work. Nothing stopping you doing training in manual mode i.a.w. the Service Letter.

For training nothing stopping you.In case of real failure of FADEC the red light on should stopping you.

Surely there are only 2 throttle positions idle and flight ?

By selecting "manual" and moving the throttle out of the flight detent, you mechanically control the fuel flow through a rack & pinion mechanism linked to the twist grip. This is the "backup" if the single FADEC channel fails. In normal operation though, you're right, there's just "idle" or "flight" and fuel flow is controlled by the FADEC.

That was what I erroneously said in the thread, 17 years retired does things to the memory, I would assume the 350 would be the same as the Huey, memory now recalls we did manual throttle circuits, procedure was to roll the throttle to idle while on the ground, as N1 approached idle flip the switch from GOV to MANUAL, wind up to flight RPM with throttle and proceed with circuit, 212 & 412 same same but only one engine in MANUAL.

It's funny - While I was reading through the last thread I was able to find an AS350B3 RFM online in 30 seconds (despite the thread starter bemoaning the fact that he no longer had access to one) and when I came to post a response I discovered that the thread had been pulled. (Plus the thread starter removed from PPrune!) My take is that you can only select the governor to MANUAL to train for emergency procedures, and the only emergency procedure the RFM describes (apart from autorotation) is how to approach and land after a FADEC failure. Once on the ground you stay there.

How far do you think you would get with Airbus or your insurers, trying to explain a cooked engine or oversped rotor?

Like this?

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=LA

How far do you think you would get with Airbus or your insurers, trying to explain a cooked engine or oversped rotor?

That is not the point......as soon as you or your company pay

The point is that I need to know how work with twistgrip in case of real failure

The B3 i fly only has idle and flight with no means of manual control, it has a
Fadec with a hydro mechanical back up in it so no means of switching off

Yes because is full FADEC (2 channel)....first models had only one

if you have a real failure in flight you follow the RFM procedure that describes how to make an approach and landing, then shut down and get it fixed. If you have a real failure on the ground you shut down and get it fixed.

Ergo, practice is bad. Therefore, in the event of an engine or tail rotor failure simply read the manual and follow the directions. I guess, these pilots didn’t read well enough?

that’s not what I said at all - practice the procedures you may have to use, don’t make stuff up and practice it.

So in this you are try to tell me that the pilot cannot have a training but just follow the RFM?

This is what 212man said in reply to:

So I don't understand why some of you question him about being allowed to practise FADEC emergencies, he even said:

So he never said you can't practice FADEC emergencies but when you do you should follow the published RFM procedures for that emergency, rather than coming up with your own procedure.
Very good advise in my book, from a very experienced pilot / instructor / examiner, who knows what he is talking about!

The US Army has been doing it this way for over 45 years. And it’s not in the RFM.
https://cimg3.ibsrv.net/gimg/pprune....ced536aeca.jpg
Manual Throttle Operation

Bolding mine, so the now deleted thread was asking a question (doing a circuit in manual throttle) that was not mechanically possible. Reading the RFM I admit to being confused on the system.

Thats correct on B3e the twistgrip is idle flight.The reason that tb^he B3 e has dual channel FADEC,on the first models of B3 was single channel FADEC, thats the reason that was a twistgrip with cable on to the fuel control.

To expand upon your post,
1. B3 (or B3 Mod) with Arriel 2B engine and single channel FADEC with manual backup.

a. Pre MOD No. 073084 has manual mechanical twist grip lock.

b. Post MOD No. 073084 has automatic electric twist grip lock.

2. B3 (sometimes referred to as B3+) with Arriel 2B1 engine and dual-channel FADEC with automatic backup.

3. B3e (designated H125) with Arriel 2D engine and dual-channel FADEC with automatic backup.