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Tiger Moth – Best of British

Tiger Moth – Best of British

On 16 December 2013, a Tiger Moth suffered a double port wing failure in Queensland’s Southport Seaway area and plummeted into the sea 300 metres off South Stradbroke Island, killing both the pilot and the passenger.

The Australian Transport Safety Bureau (ATSB) investigated this disaster and has issued a preliminary written report on aspects of its investigation on 24 February 2014.

The report has a brief summary, which encapsulates what may be the root cause of the accident. It bears repeating “Preliminary examination indicated that both of the aircraft’s lateral tie rods, which join the lower wings to the fuselage, had fractured at areas of significant, pre-existing fatigue cracking in the threaded section near the join with the left wing.”

The preliminary report went on to detail other matters of concern apparent in the operation and maintenance of the aircraft and the structure of the lateral tie rods. They are:

1.            The published report is only a preliminary report and is subject to ongoing investigations being conducted.

2.            When the left wings failed the aircraft was at the bottom of an aerobatic manoeuvre, a loop.

3.            An onboard video camera, recovered after the accident, indicated that there was a rippling effect in the lower mainplane fabric skin aft of the attachment points of the aft lateral tie rod.

4.            The aircraft was used regularly for joy rides combined with aerobatic flight.

5.            Each of the tie rods fitted to the aircraft were Australian made, by a Victorian firm, J & R Aerospace P/L under an Australian Parts Manufacturing Authority (APMA) issued by CASA or its predecessors.

6.            The pre-existing cracking was about 50 per cent in the forward lateral tie rod and 70 per cent in the aft lateral tie rod at the beginning of the threaded section in each case.

The preliminary report went on to describe prior occasions when lateral tie rods had failed or when other Tiger Moth aircraft had suffered wing failures. In the UK in 1996 during routine maintenance activity a UK registered Tiger was found to have sustained a lateral tie rod fracture at the thread root. Subsequent examination found there was significant pre-existing fatigue cracking at the point of failure. At that time there were no requirements in place for these vital components.

After the UK tie rod fracture, the UK regulator decided to give the components a “life” of 18 years or 2000 hours. A Technical News Sheet no 29 (TNS) was issued to raise the service life and to institute a procedure for examination of the rods following (a) a heavy landing (b) undercarriage trauma and (c) the annual inspection. The News sheet went on to detail an inspection regime including looking for elongated holes in attachment points or ovalling of the rods among other matters. The TNS was followed up by a UK AD 006-10-97 and subsequently CASA issued AD/DH82/10 amendment 1 on June 1999 which reflected the UK AD.

The Australian AD seems to have either watered down the inspection regime or did not mandate any comprehensive NDT testing or examination of the lateral tie rods.

Two other Australian Tiger Moth wing failure accidents were considered, VH-TMK and VH-AJG. VH-TMK occurred because the upper right wing spar was weakened as a result of fungal decay of the wooden spar and a partially de-bonded doubler. Certainly not a lateral tie rod failure. VH-AJG accident was not attributable to an inflight break-up.

The accident tie rods were examined by a metallurgist and it was found that the rods’ hardness was consistent with the required strength level. There was some discussion in the report about the nature of the screw thread development. The Australian rods were cut with a die as had the UK rods earlier and not by production rolled threads. The VH-TMK rods had been fitted for 11 years and had 700 hours of life to run.

The ATSB preliminary report was redolent with “feel good” comments rather than a direction to do something positive to prevent a recurrence of lateral tie rod failure. ATSB was not sure if the accident was caused by lateral tie rod failure or other wing failure criteria (the summary). Relevant organisations are ENCOURAGED to initiate proactive safety action to address safety issues (page 23). Bodies should address COSTS and BENEFITS of any particular means of addressing safety issues (page 23) ATSB may issue safety advisory notices SUGGESTING an organisation CONSIDER a safety issue and take action where it BELIEVES it appropriate (page 23). These recommendations do not define a positive path to ensure safety as a matter of law.

The report was sent to the Original Equipment Maker (OEM), De Havilland Support P/L, a subsidiary of British Aerospace Ltd. They immediately took a positive step. They, in conjunction with UK CAA, issued an Emergency Aircraft Directive G-2014-0001-E on 21 March 2014, about a month after the ATSB preliminary report. The UK AD stated that “this AD is mandatory for applicable aircraft registered in the United Kingdom”. It contained an effective date, 21 March 2014 and in summary said “buy British lateral tie rods for Tiger Moths” and remove and destroy Australian ones. Not much more than that.

The UK AD did not specify any in situ inspections, did not outlaw cut threads as opposed to rolled threads; did not require any testing of removed rods; did introduce an aerobatic restriction until the provenance of the tie rods had been checked. It also introduced a 10 hour flight restriction from the effective date until the rods are verified as British or removed and destroyed if not British.

CASA brought in a PROPOSED AD/DH 82/17 paraphrasing most of the UK AD but leaving out the effective date. Additionally, This AD suspended all aerobatic flight of Tiger Moths permanently until fitted with British tie rods. Again no NDT testing of Australian tier rods, no in situ testing, no consideration of how the aircraft had been operated in the past, nothing about “undercarriage trauma”, heavy landings, ground loops or impact damage. Just “buy British”. No thought was given to the fact that the only other recorded incident in respect of the lateral tie rods was a fracture of a British lateral tie rod in July 1996.

It seems that as an inflight accident occurred during aerobatics in Queensland in a Tiger Moth any lateral tie rods that are made in Australia and not made in UK under a PMA issued by the UK CAA are verboten. What price for an organisation that takes the ATSB at its word and addresses the COSTS and BENEFITS of the safety issue or CONSIDERS the safety issue and takes action which it BELIEVES is appropriate and wants to use readily available Australian lateral tie rods at a more reasonable cost and availability?

The fact that the UK PMA manufacturers cannot supply lateral tie rods for the 217 DH82 aircraft in the immediate future of the promulgation of PAD/DH82/17 seems to have escaped everyone’s consciousness.

CASA wrote to all operators by open letter dated 24 March 2014. This letter stated “that under regulation 39.001A of the Civil Aviation Safety Regulations the UK AD is considered to be an Australian Airworthiness Directive (AD) as the UK CAA is the State of Design for the DH-82 aircraft.” It is a moot point that the Commonwealth has the power to declare that a foreign law, UK ADs, are ipso facto Australian law. Usually, some activity in a Parliament is necessary to give a directive the power of law operative in Australia. Be that as it may, the UK law stated that the UK AD was mandatory for UK registered aircraft but does not mention Australian registered aircraft.

Why is any of this of relevance to operating pilots and engineers of Tiger Moths in Australia? It so happens that a LAME was asked by an operator to check his Tiger Moth and the rods and additionally, to repair its fabric as it was “tired” (read “tatty”). The Tiger was in Central Queensland and the LAME came from Western Victoria to look at it. The lateral tie rods were inspected and found to be J & R Aerospace P/L rods, but were in surprisingly good condition. The tightness of the retaining nuts were checked. The surrounding positioning and paint of the H Point was found to be sound. The aircraft had not suffered any known “undercarriage trauma”: had not been ground looped as the Southport was reported to have been. Patches were placed on the tatty bits of fabric after the underlying wooden spars were checked. The aircraft was given a thorough pre flight by the LAME who was also the ferry pilot.

He set off and passed through various airfields where he refuelled or stayed overnight. At each stop the LAME did another lateral tie rod inspection to see if there was any movement in either the rods or the H point for each rod. At one stop, weather intervened and the LAME/pilot stayed on the ground rather than risk flying in turbulent air that may trigger problems with the lateral tie rods and cause his death.

Unfortunately, on arrival at an airfield in Victoria, our ferry pilot was met by a Sports Aviation technical officer of CASA. Refuelling from jerry cans, using mogas, not calling on the radio in a CTAF area, the general tattiness of the aircraft, whether the pilot had maps, GPS and an ERSA and other non specific CAR 30 offences were canvassed, failure to complete entries of dailies in the maintenance release and essentially the lateral tie rod fitment became paramount. Naturally, the LAME/pilot was alarmed and gave one less than truthful answer.

The LAME, who conducts a moderately large workshop was required to attend a meeting at CASA’s convenience. He asked for assistance. His licence, medical, log book, maintenance release and aircraft log book were required to be produced prior to the hearing. No written outline of what would occur at the hearing was disclosed. He had to attend for investigation.

Clearly, the flying time from Central Queensland to the Victorian Border was in the order of 15 hours in a Tiger Moth and clearly, the UK AD 10 hour limit was exceeded. The CASA PAD did not have an effective 10 hour limit in it and the UK AD, even if it could be accepted as Australian law, did not specifically apply to Australian registered Tiger Moths. They both accepted this. It was also accepted that the poor condition of the aircraft was within the capability of the LAME to determine or assess and as he had flown for 15 hours or so in that condition without incident there really was nothing to charge him with. After all he was a person who could determine the extent of technical risk that he was running and he was taking it to his workshop to re fabric the aircraft a remedy that he could not apply at the operator’s site.

However, it was decided that as he had done very few navigation exercises in the recent past and he had admitted that he did not use radio in a CTAF  he would have his pilot’s licence suspended for a period of training, he would undergo a flight test and then he would be counselled and have his pilots’ licence restored. The LAME accepted this situation.

The human element may have been dealt with in a fashion. Nevertheless, an elephant in the room still existed in respect of the lateral tie rods per se. The safety regulator did not consider in depth just why the rods had broken. Both the UK and Australian authorities put their head in the sand and said only British manufactured lateral tie rods had the inherent integrity to ensure that the wings would not separate from any Tiger Moth in future.

The evidence of the 1996 British fractured tie rods was ignored. The Tiger Moth was considered a good aerobatic aircraft and yet at Southport during about a minute of aerobatics the wing separated. Was this a major contributing factor in the accident? After the fitment of British tie rods Tiger Moths can now be flown aerobatically. The LAME involved in the above CASA investigation had serviced many Tiger Moths over about 20 years. He actually had a set of Australian lateral tie rods that had run the full life of 2000 hours or about 18 years in his workshop. He had them tested by a metallurgist and they were found to be sound even after their life had expired. Neither the UK nor the Australian authorities had undertaken any research on any current Australian or UK fitted tie rods to determine if cracking was present in any Tiger Moth. No one considered requiring any magna flux or dye penetrant testing of currently fitted tie rods. Just ban all APMA tie rods completely.

Certainly, ATSB have indicated that the investigation is still open. Are they going to investigate whether the Tiger Moth in question had suffered any “undercarriage trauma” that may have caused the cracking? Are they going to investigate whether flick rolls in the aircraft was a cause of the break up? Are they going to stress test the wing structure to determine why just prior to the break up there was rippling in the fabric of the left lower mainplane aft of the lateral tie rods? Was this rippling caused by a defect in the wooden main spar of the wing the initiating prime cause and the lateral tie rod fracture merely a secondary effect of break up?

Or are we going to simply “Buy British” and fit UK tie rods to the detriment of Australian manufactured tie rods? Should an accident occur in another light aircraft, not necessarily a Tiger Moth, which has an APMA part fitted will all APMA parts be banned and only USA or European manufactured parts be used henceforth?

Watch this space…

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