Writer's response
Most people who regularly read newspapers understand that it’s not journalists, but subeditors, who write the headlines. Their quite valid purpose is to attract the reader’s attention, which works, and they don’t usually tamper with detail in the text except to correct things like grammar and style.
No apologies should be expected for reporting on events that have become topical as a result of recent accidents.
Would anybody care to challenge any of the following facts? All material assertions in the article are supported by documents in my possession.
When a wing or wings, or other major airframe components separate from an airframe in flight, a structural failure has occurred.
All events related to changed Shrike maximum weights occurred before Coastwatch contracts became an issue. The aircraft were imported second-hand by one Jim Wilson and (from memory) his company was called Executive Air Services.
The Shrike Commander 500-S and -U were never certificated in their country of manufacture at any weight higher than 6,750 lb. (I apologise in advance for the use of pounds instead of kilograms but all the documentation is in pounds which were fashionable at the time.)
For 25 years the type has been approved for operation in Australia at MTOWs of 7150 lb IFR and 7400 lb VFR, under an Australian STC issued by the regulator (then the Department of Aviation) in June 1971 when the aircraft were first imported into Australia.
It has been my experience that aircraft approved at a particular MTOW quite frequently take off at that weight.
Manufacture of the Aero Commander 500-S and -U ceased in the early eighties.
The Department of Aviation never made available any flight test data or structural analysis to support the higher STC weights.
The weights were challenged in 1982 when the Government Aircraft Factory’s chief test pilot flew a Shrike against the Australian certification requirement, which as we all know, with the possible exception of the occasional junior lawyer, is that it demonstrate capability to climb with the critical engine inoperative at a one per cent still air gradient in a standard atmosphere, following a takeoff at MTOW.
The test pilot reported that extrapolation of the published data revealed that at 7,150 lb the aircraft failed to meet the requirement by 0.5%. The test flight results showed a worse result. At 6,750 lb the average gradient was 0.85% short of the criteria, and at 7,150 there was a nett deficiency of 1.3%
When told of the performance figures on which the STC was based, Gulfstream American Corporation’s performance engineers didn’t believe the aircraft could be flown to perform 10% better. One of these made two comments:
“We could sure use a test pilot with that kind of talent,” and
“If we’d thought it could have performed to a higher weight, we’d have certified it at that weight, sold a lot more airplanes, and made a lot more money.”
The outcomes of the GAF tests are reflected in the following report by consulting aeronautical engineer Malcolm McLeary: “On the information supplied there appear to be three good reasons why a review is warranted:
The manufacturer has not designed or the State authority of origin has not approved the operation to the higher all up weight figures. The higher weights were unilaterally taken by Australia only.
The flight tests of an Aero Commander carried out by GAF show non-compliance to the certification standards; and
The power loading for the type [weight per available horsepower] is suspiciously high when compared to other aircraft supposedly designed to meet the same requirements.”
And further: “Probably worth noting is the fact that if the power available is just sufficient to meet the minimum performance standards with a TOW max of 6,750 lb, the additional power required to meet the same performance standard at a TOW max of 7,150 lb (Australian Certification) is 14.8%. That is to say, for an approximate 10% increase in TOW, the additional power required is about 15%. Arguing further, if the Aero Commander was able to just satisfy the applicable certification standards at the higher TOW of 7400 lb then at 6750 lb the aircraft would need reserve power of approximately 15%. This would indicate that the flight test aircraft had in fact degraded by over 20%, which is unlikely.
The regulator of the day sought to explain the discrepancy between test flight results as the performance differences between a new and a used (3,090 hour) aeroplane. The Gulfstream American Corporation performance engineer rejected the suggestion that the performance of an aircraft that had flown only a little over 3,000 hours could be degraded by 20%: “Well, maybe if it was run over by a bulldozer,” he quipped.
McLeary further commented: “The D.O.A. exists to safeguard the established standards. I believe that they have no option but to reconsider the performance limits of the Aero Commander if written evidence to support the claim is presented. It is a serious enough deviation from the manufacturer’s limits for you to insist on a performance audit, even if it means by-passing the D.O.A. officers and going direct to the Minister.”
A detailed draft of a feature article covering these issues was provided to CASA for comment, and has also been provided to ATSB for its information and assessment. This comment contains its salient points.
CASA, when asked, was unable to cite another single example in which a factory-delivered standard aircraft without aerodynamic or power train modifications, had been certified in this country at a higher MTOW than in its country of certification.
SUMMARY:
Nigel Johnson, a now-retired lifelong GA pilot and senior manager with considerable Shrike Commander experience, comments: “This whole saga is a sad reflection on the competency of government organisations to involve themselves in the more technical aspects of aviation. It has involved three government agencies – an aircraft factory, a bureaucracy set up to guard our coastlines, and the aviation regulator which has changed its name and organisational structure countless times during these events. Almost everything each of these agencies has done during the whole episode, has had the potential to add to aviation’s death toll. No politician of any party has shown any meaningful interest in the complex problems that have been identified, and it seems that even more Shrike Commanders will have to crash before somebody does something about it.
“Although it might mean acknowledging past mistakes, a long-standing CASA aversion, that will need to happen before bureaucratic obstruction and inertia stop killing passengers and pilots.”
Apart from regulatory officials, nobody with whom I have discussed this issue believes that the process by which the STC was issued was a valid one.
Readers are invited to suggest possible conclusions that suggest an alternative explanation other than negligence or deception. I would welcome the opportunity to discuss and if necessary report on any other explanation.
(Edited only to include para breaks. T.W.)
Last edited by tail wheel; 16th Aug 2007 at 00:59.