AD/GBK 117/21 Pressure Altitude Limitation and Max N1 Check (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 BK 117 Series Helicopters

AD/GBK 117/21 Pressure Altitude Limitation
and Max N1 Check 9/2008

Applicability:

EUROCOPTER DEUTSCHLAND MBB-BK 117 C-1 and C-2 helicopters except those aircraft on which both engines have been modified in accordance with Turboméca Modification TU358.

Requirement:

1.    Affix the selected placard and amend the Flight Manual (FLM) in accordance with the instructions of the referenced Alert Service Bulletin.

2.    For helicopters that are about to perform starting, landing and hovering procedures in or out of ground effect at pressure altitudes above 10,000 feet and/or flights at pressure altitudes above 13,000 feet, accomplish the “MAX N1 CHECK” to establish the OEI rating of the engines in accordance with the instructions of the referenced Alert Service Bulletin.

3.    Repeat the “MAX N1 CHECK” to establish the OEI rating of the engines in accordance with the instructions of the referenced Alert Service Bulletin.

4.    If the OEI rating is not reached, only operations at pressure altitudes up to a maximum of 10,000 feet and mission flights at pressure altitudes up to a maximum of 13,000 feet may be conducted. Amend the placard and FLM accordingly.

5.    Repeat the “MAX N1 CHECK” to establish the OEI rating of the engines in accordance with the instructions of the referenced Alert Service Bulletin.

6.    Remove the placard and FLM changes from the helicopter.

       Once modification TU358 is incorporated into both Fuel Control Units (FCU)’s the “MAX N1 CHECK” is no longer required.

7.    Do not install a spare FCU on any helicopter as a replacement part unless it has been modified in accordance with Turboméca modification TU358.

Eurocopter Deutschland Alert Service Bulletin (ASB) No. ASB-MBB-BK117-60-121 Revision 4 pertains to the requirements of this AD.  The use of later approved revisions of these documents is acceptable for compliance with the requirements of this AD.

Note:  EASA AD 2008-0061 dated 27 March 2008 refers.

Compliance:

1.    Within 30 days after the effective date of this AD, unless previously accomplished.

2.    Before the next such mission after the effective date of this AD.

3.    Within 600 Flight Hours (FH) after the effective date of this AD and thereafter at intervals not to exceed 600 FH.

4.    From the effective date of this AD.

5.    When, after failing to reach the OEI rating, and either the engine, the FCU, engine module 2 and/or engine module 3 is replaced.

6.    After modification of both FCUs in accordance with Turboméca modification TU358.

7.    After 10 April 2009.

This Airworthiness Directive becomes effective on 28 August 2008.

Background:

Prior to delivery of each helicopter, Eurocopter Deutschland performs the “MAX N1 Check” at a pressure altitude (PA) of about 10,000 feet.  During supplementary testing the “MAX N1 CHECK” at maximum certification altitude, a few MBB-BK 117 C-2 helicopters could not reach the specified N1 power threshold value.  The cause was identified as an engine acceleration limitation due to a delivered fuel flow lower than the engine fuel flow demand to achieve the OEI rating at high altitude.  The fuel flow is limited by the FCU acceleration law in those cases.  This limitation could potentially occur at altitudes exceeding 10,000 feet, depending on the engine and FCU characteristics.  As a conservative measure, TURBOMECA and EUROCOPTER decided that take-off, landing and HIGE (Hover In Ground Effect) and/or HOGE (Hover Out of Ground Effect) operations above 10,000 feet or level flight above 13,000 feet require a dedicated mandatory check.

Turboméca has now developed a modification (TU358) that will, when accomplished on both engines installed on the helicopter, cancel the required checks and allow the removal of the placard and flight manual changes.

James Coyne
Delegate of the Civil Aviation Safety Authority

17 July 2008