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Recommendation issued to: Civil Aviation Safety Authority

Recommendation details
Output No: R20020134
Date issued: 12 December 2002
Safety action status:
Background:

The ATSB does not have the resources to carry out a full cost-benefit analysis of every recommendation. The cost of any recommendation must always be balanced against its benefits to safety, and aviation safety involves the whole community. Such analysis is a matter for the body to which the recommendation is addressed (for example the Civil Aviation Safety Authority in consultation with the industry).


FACTUAL INFORMATION

Background

On 23 March 2001, a New Zealand registered Hughes 500D helicopter, ZK-HMN, sustained an in-flight engine flameout that necessitated a forced landing near Milford Sound, New Zealand. The pilot and observer, the only occupants, escaped uninjured, however the helicopter was substantially damaged. The New Zealand Transport Accident Investigation Commission (TAIC) conducted an investigation of the accident (TAIC Investigation Report 01-003 refers). The helicopter's engine, an Allison model 250-C20B, serial number 821211F, with 8,066 hours time since new (TSN) was removed to an Australian test facility for engine test runs, with a representative of TAIC attending. The results of the test run indicated an anomaly in the fuel control unit (FCU).


FCU initial test rig testing

FCU part number 2924644-29, serial number 336660, with 1,400.25 hours time since overhaul (TSO), was removed and tested at an authorised Australian overhaul facility. Upon testing, the FCU could not be operated successfully and failed the maximum governor spring setting test point (TP) number 9.000. After consultation with the FCU manufacturer, the FCU was partially disassembled to allow internal examination. During the examination of the FCU, it was noted that the flyweight clip adjustment appeared to be out of tolerance. The clip was adjusted to the specified clearances and the test continued. The FCU was then successfully operated and tested.


FCU background

The FCU was overhauled on 28 December 1996 by an Australian overhaul facility. Following overhaul, it was certified as passing all tests on the test rig as required by the FCU manufacturer. It was then installed on the engine of ZK-HMN on 17 March 1997. On 31 December 1997 it was removed after completing 238.5 hours TSO, for rectification of a defect which was entered in the logbook as 'Constant operation at 110% N2 (power turbine speed)'. The FCU was then shipped back to the same overhaul facility for repair. Upon induction testing, the FCU could not be successfully operated and failed the maximum governor spring setting TP, among other test parameters. Further examination revealed two 50mm cracks at the FCU drive governor body housing, and a resulting air leak. The overhaul facility recommended a complete overhaul of the component. Subsequently, on 3 July 1998, the FCU was partially stripped to replace the drive governor housing, with all seals that were disturbed replaced. A review of the FCU documentation indicated that the FCU was then successfully tested and shipped back to the operator.

On 31 July 1998, the FCU was reinstalled on the engine of ZK-HMN, replacing a loan component. The engine had operated 162.0 flight hours with the loan FCU installed. There were no discrepancies annotated in the helicopter or engine logbooks referring to any N2 anomalies while the loan component was installed. During the next 1,000.3 hours of engine operation, the operator removed and replaced the Power Turbine Governor (PTG) three times attempting to resolve a discrepancy of engine N2 drooping and hunting.


FCU flyweight clip

Examination of the flyweight clip of the subject FCU during technical disassembly revealed that the clip may have never been physically adjusted. The flyweight clip adjustment of the component set the travel limits of the FCU flyweights in order to adjust fuel flow according to engine RPM and power demands. The nominal adjustment of the flyweight stop clips and the flyweight levers during overhaul or repair, according to the manufacturer's manual were '0.100-0.105 inches' clearance. The measured dimensional clearance between the flyweight stop clips and the flyweight levers of the accident FCU when checked were .042 and .044 inches (measuring two sides). That value correlated to the measurements of a new, unadjusted, flyweight clip.


FCU testing

FCU testing following overhaul or repair was completed on a calibrated test rig to ensure acceptable levels of performance. The test measured RPM, fuel flow, pressure, throttle speed, and airflow against manufacturer provided performance values referred to as Test Points (TP). According to the FCU manufacturer, with the flyweight clip adjusted as found on initial technical disassembly examination following the accident, the component would not have successfully passed TP number 9.000. During testing of the component prior to the technical disassembly examination, and during an earlier induction for repair, it did not successfully pass TP number 9.000.


FCU overhaul facility documentation examination

Overhaul facility documentation was examined for indications of component testing results. According to the documentation, the FCU passed all tests on the test rig following both overhaul and repair of the component, including TP number 9.000.

The overhaul and repair documentation listed values to record the clearance between the flyweight stop clips and the flyweight levers. The repair documentation listed the recorded measurement as 0.101 inches. The overhaul documentation listed the recorded measurement as 0.100 inches. According to the FCU manufacturer's published requirements, both were considered as acceptable measurements. Neither the overhaul, nor the repair parts list documentation for the component, annotated a replacement flyweight clip as being installed.


Foreign airworthiness regulator surveillance

The United States of America (USA) Federal Aviation Administration (FAA) conducted regular surveillance of the overhaul facility because of the use of overhauled and repaired components of that organisation in aircraft registered in the USA. They informed the Australian Transport Safety Bureau (ATSB) that in 1997 they had revoked the facility's FAA Air Agency certificate because the facility did not conform to FAA regulations. The FAA further advised that, in December 2000, following several management and personnel changes within the overhaul facility, a total certification inspection was completed and the Air Agency certificate was reinstated.


Australian Civil Aviation Safety Authority surveillance

The Australian Civil Aviation Safety Authority (CASA) provided the ATSB with all surveillance files of the overhaul facility available at the time of the request. According to the provided files, the last surveillance of the organisation prior to the overhaul date of the FCU was 13 February 1996. Following that audit, three Non-compliance Notices (NCN) were issued outlining discrepancies. On 17 December 1997, another audit was conducted with two NCNs issued. On 16 June 1998, another audit was conducted with one documentation discrepancy noted. On 30 September 1998, another audit was completed with one documentation related NCN issued. On 16 April 1999, another NCN was issued citing no corrective action following an internal audit. There was no documentation found on the provided files annotating the revoking of the facility's FAA Air Agency certificate in 1997. CASA also advised that there was no formal mechanism through which CASA would be advised of the results of any surveillance action taken by a foreign airworthiness agency on an Australian Certificate of Approval holder.


ANALYSIS

Physical evidence following the technical examination of the fuel control unit (FCU) revealed that the flyweight clip had not been manually adjusted to the required value. However, assembly documentation for the repair and overhaul of the component had annotated that the flyweight clip had been adjusted and that the dimensions were within acceptable limits.

The operator reported that the engine had operated with anomalies in the N2 (power turbine speed) following both the overhaul and repair of the FCU. Following the overhaul, upon removal for repair, cracks were found in the governor (drive body) housing that affected normal operation of the FCU. The reason for the FCU not passing TP number 9.000 during the induction testing prior to repair may have been due to the cracked governor (drive body) housing.


CONCLUSION

The flameout of the engine of ZK-HMN was most likely a result of internal anomalies of the engine FCU. The FCU was found to have a replacement flyweight clip installed that was not adjusted to the manufacturer's specifications. The investigation could not conclusively determine when the flyweight clip was replaced with the unadjusted clip.

Currently, there are no formal protocols for foreign regulatory agencies to provide CASA with the results of an audit inspection of an Australian Certificate of Approval (C of A) holder that is also approved by that foreign agency. Information concerning the results of those audits could provide valuable information for use in CASA surveillance of Australian C of A holders.

As a result of this occurrence, the Australian Transport Safety Bureau issues the following safety recommendation:

Output text

The Australian Transport Safety Bureau recommends that the Australian Civil Aviation Safety Authority consider formalising a method to obtain and review the results of any foreign airworthiness authority audit of Australian Certificate of Approval holders.

Initial response
Date issued: 16 July 2003
Response from: Civil Aviation Safety Authority
Action status: Monitor
Response text:

The Authority has written to the United States Federal Aviation Administration, Transport Canada, the United Kingdom Civil Aviation Authority and the New Zealand Civil Aviation Authority to initiate discussions. The discussions are aimed at establishing an arrangement or protocol between the Authority and those agencies that will enable the Authority to obtain the results of any surveillance or audits that those agencies might carry out in relation to Australian Certificate of Approval holders.

The Authority intends to liaise separately with the Joint Aviation Authorities (JAA) to ascertain whether it is appropriate to initiate similar discussions at this time or to defer this until after commencement of the new European authority, the European Aviation Safety Agency (EASA). EASA is due to commence business on 28 September 2003 and will progressively take over the functions and activities of the JAA. The authority shall keep you informed of responses and outcomes in due course.

Further correspondence
Date issued: 19 December 2003
Response from: Civil Aviation Safety Authority
Response status: Monitor
Response text:

I refer to your request for additional information in support of CASA's response to Recommendation R20020134.

I am advised that in July 2003, CASA wrote to a number of other foreign regulatory authorities with a view to initiating discussions aimed at establishing an arrangement or protocol between CASA and those authorities that would enable CASA to obtain the results of any surveillance or audits that those authorities might carry out in relation to Australian Certificate of Approval holders. To date, however, CASA has had little substantive response from the authorities.

I understand that the New Zealand Civil Aviation Authority (NZ CAA) acknowledged the request and agreed in principle that such an arrangement might be possible, subject to more detailed consideration, but noting also resource constraints at the time. No further advice has subsequently been received.

The United Kingdom Civil Aviation Authority (UK CAA) noted that the issue would cease to be applicable by the end of September 2003 when the new European Aviation Safety Agency (EASA) came into force, and recommended that we take up the issue with EASA after that date. Transport Canada and the United States Federal Aviation Administration (US FAA) have not responded formally, although an informal discussion with an FAA office indicated that the matter may be problematic and had been referred for further consideration. CASA is continuing to laise with these authorities, and with EASA now that it is established, to progress this matter. Noting that action to progress this matter rests with other Agencies as well as CASA, we will keep you informed as this matter progresses.

Further correspondence
Date issued: 11 April 2007
Response from: Civil Aviation Safety Authority
Response status: Closed - Not Accepted
Response text:
ATSB response:

No further response from CASA

Further correspondence
Date issued: 04 February 2003
Response from: Civil Aviation Safety Authority
Response status: Monitor
Response text:

The Authority accepts the Recommendation and advises that the Authority will consult with the relevant foreign airworthiness authorities with a view to formalising an arrangement to obtain the results of foreign audits of Australian Certificate of Approval holders.
The Authority intends writing to the United States Federal Aviation Administration, the United Kingdom Civil Aviation Authority, Transport Canada, the New Zealand Civil Aviation Authority and the Joint Aviation Authorities. The Authority undertakes to advise the ATSB of progress against this recommendation as this matter develops.

 
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Last update 03 April 2012