AD/Dauphin/98 Vertical Gyro Unit Data Output Operational Limitation/Procedure (Cth)

AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998.  The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Eurocopter SA 360 and SA 365 (Dauphin) Series Helicopters

AD/DAUPHIN/98 Vertical Gyro Unit Data Output - Operational Limitation/Procedure 13/2008 TX

Applicability:	AS 365 N3 helicopters, all serial numbers, equipped with the vertical gyro units GV76-1 installed on the rear left hand (LH) rack, performing flight in Instrument Meteorological Conditions (IMC) conditions or under Instrument Flight Rules (IFR) or night Visual Flight Rules (VFR).
Requirement:	1.    Flight in IMC or night VFR is prohibited if one or more of the following equipments is/are not fully operative:
a.     autopilot channels,
b.    flight coupler, and
c.     stand by horizon.
2.    If the autopilot channels, the flight coupler and the stand-by horizon are fully operative in both the single-pilot and the two-pilot configuration, the operational procedure described in paragraph 2.B. of Eurocopter Emergency Alert Service Bulletin (EASB) No. 01.00.61 dated 23 October 2008 or later Revision approved by the European Aviation Safety Agency (EASA) must be accomplished at intervals not exceeding 5 flying minutes during the flight phases in IMC conditions (IFR) or night VFR without visible horizon.
Compliance with this Directive may be accomplished by inserting a copy of this Directive into Section 4-8 “Special operating procedure” of the Aircraft Flight Manual (AFM).
Note:  EASA Emergency AD 2008-0195-E refers.
Compliance:	For Requirements 1 and 2 - After the effective date of this Directive.
This Airworthiness Directive becomes effective on 27 October 2008.
Background:	On a AS 365 N3 helicopter, a slow drift in the roll axis was simultaneously noted in flight on the pilot’s and co-pilot’s horizons of the flight control displays.  As this drift was in the same direction and at the same rate, the automatic flight control system and the display system indicated no deviation to the flight crew.

Investigation has shown that only AS 365 N3 helicopters equipped with vertical gyros GV76-1 installed on the rear rack of the helicopter are concerned by the drift.  Considering that vertical gyro units process roll as well as pitch data, simultaneous drift in both GV76-1 units may occur on both axes (roll and pitch), independently or at the same time, which constitutes an unsafe condition.

Pending the availability of a corrective action aimed at precluding any risk of drift on the pilots’ horizons occurring at the same time and in the same direction, this Directive mandates an operational limitation and an operational procedure for all flights in IMC (IFR) or night VFR.

James Coyne
Delegate of the Civil Aviation Safety Authority

24 October 2008