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?