The CAS program was important in that it might have detected the recurring trim drive wear problem early on and focused more attention on it. The cause of the accident was found to be a negligently maintained stab trim drive. There was a lack of proper lubrication and excessive wear on the acme threaded drive mechanism. The FAA and the NTSB opined that a properly functioning CAS system might have detected the dangerous nature of this fault before the accident occurred. (It’s interesting to note that the J3 Cub I flew many years ago has a similar acme threaded hand crank operated stabilizer trim mechanism.)
Needless to say, there was an order for all inspectors to pay special attention to FAR 121.373. The FAA further ordered a special inspection of 25 major airlines to determine the state of their CAS programs. The results of these special inspections were so controversial that the FAA refused to release them for almost two years. The CASS became a primary focus of FAA inspectors assigned to air carriers. At last, some attention.
Chalks Ocean Airlines
A few years later in December 2005, a Chalks Airlines turboprop Grumman Mallard lost a wing shortly after it took off and crashed near Miami, FL. Structural failure of the wing was cited as the obvious cause.
The NTSB found that “…Chalks maintenance program and practices were deficient, and these deficiencies were causal to the accident.” Again, another clearly continuing maintenance analysis application.
Chalks was an FAR 121 air carrier and did have an FAR 121.343 CAS program set out and described in its maintenance manual. The program was an approved maintenance program that included a quality control function that, in accord with the regulation, is designed to continuously monitor the program and catalog maintenance discrepancies. The conclusion by the accident board was that the system just did not work and that it did not track discrepancies. The Board said that both maintenance and oversight (surveillance by both the company and the FAA) was not adequate.
The Board elaborated by saying that the wing separation was a result of the failure of Chalks maintenance program to identify and properly repair fatigue cracks in the wing, and the failure of the FAA to detect and correct deficiencies in Chalks maintenance program.
Here again, an FAR mandated inspection and analysis system did not work. Although the Board in its report was kind to both the operator and the FAA personnel when it stated further that the FAA’s mandate was a “one-size-fits-all” approach that should be expanded to add more detail in just what the carriers should address. The Board went on to say that the inspectors’ guidance from the FAA did not account for specific risk factors (saltwater for Chalks).
The so-called “risk factors” were all too evident! 1. Older aircraft, (most of the Mallards were built in 1947) although re-engined with PT-6’s in recent years. 2. Saltwater an all too obvious risk factor for corrosion and deterioration of structural components. This writer started flying in Luscombe 8F and Piper PA 18 floatplanes. Saltwater corrosion was an all too obvious risk and very evident. We were required to wash down all aircraft after flight with fresh water when returned to the ramp. Nonetheless, you could frequently find spots under the aluminum wing of a Luscombe where you could poke a pencil through the corroded aluminum skin. The spars were frequently looked at and protected with anti-corrosion liquids as far as could be done with the wings in place. Wing skins were frequently replaced. The fabric surfaces of the PA 18 faired much better in this regard although other steel parts bore the brunt of corrosion from saltwater. Engine parts faired little better. Exhaust manifolds, frequently leaked. There is no let-up to saltwater corrosion. All you can do is slow it down.
Chalks Mallards wings had integral fuel tanks. Any fuel leak meant that the integrity of the wing could be compromised in the area of the leak. Every fuel leak does not mean a structural problem but they must be cataloged and of course sealed and inspected where necessary. The Board urged that all leaks and other structural deficiencies should have been tracked carefully by Chalks. Here again, the CASS failed.
Modern airliners have integral fuel tanks in the wings. The sealing methods and material however are probably much improved since 1947 when the Mallards were built. Even the Convair series of piston and turbines (240, 340, 440, 580, 5800) are all wet wings with integral fuel tanks. They are prone to wing fuel leaks as well. The Convairs were built like battleships, that’s why many still fly today. Most are not of course exposed to saltwater.
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