Lessons not Learned From The Past – Part 4
Guest Editorial written by David H. Marion — The NTSB eventually judged that the official “Probable Cause” of the crash of N2969 was “(1) the failure of the Chalk’s Ocean Airways maintenance program to identify and properly repair fatigue cracks in the right wing and (2) the failure of the FAA to detect and correct deficiencies in the company’s maintenance program.” Doesn’t that sound very similar to the “probable cause” of the Antilles Air Boats crash in September 1978 as discussed in Part 2?
Unlike the Antilles Air Boats crash however the evidence is not as clear that the maintenance “failures” were quite so intentional at Chalk’s. Even so, the number of pilots interviewed during the post-crash investigation who were concerned or worried about insufficient, ineffective, or inappropriately deferred maintenance was three or four times the number of Chalk’s pilots who were happy or satisfied with it. Several former pilots in fact had even gone so far as to quit working for Chalk’s over the issue of poor maintenance. I would call that a serious “red flag” that something there was not right.
The most common complaints were that maintenance was either deferred or delayed too many times or that it was not effective when it was supposedly done. One of the most common squawks was persistent fuel leaks that had to be written up several times usually over the course of a couple of days in a row before any action was taken. While there was less evidence of intentional neglect, there was still some evidence that pilots were tacitly pressured fly aircraft that had not been fixed or that mechanics in some cases falsely recorded maintenance that had not actually been done – or almost just as commonly that was done, albeit incorrectly. Falsified maintenance records, or as noted in Part 3 suspiciously “missing” maintenance records, are additional “red flags.”
Something else that stood out in the course of the investigation is that Chalk’s Director of Operations seemed to have relied too heavily on paperwork and failed to have any sense of the actual status or physical condition of the aircraft. It also seemed from testimony of other company personnel that there wasn’t enough appreciation for the severity of the maintenance problems and especially the corrosion issues being experienced with the fleet. One maintenance supervisor apparently described the recurring wing skin cracks as only “superficial” and that seems to indicate a complete lack of understanding of the concept of the semi-monocoque construction used to build airplanes like the Mallard. These kinds of lack of concern or awareness are more “red flags.”
Semi-monocoque construction is also known as “stressed skin” construction because the internal framework bears only part of the structural loads – and the skin bears the rest. While normal “land” planes have shock absorbing mechanisms built-in to their landing gear, seaplanes and flying boats in particular are subject to all of the impact stress and strain of contact with the water at for example 80 mph without any shock absorption whatsoever. They are also subject to repetitive pounding from waves – and all of that is transmitted directly to the primary structure of the aircraft.
In its heyday, Grumman had a well-deserved reputation as “the Ironworks” because it built such tough aircraft and compared to landplanes, their flying boats in particular had probably three or four times as much internal framing and reinforcement. Remember though if you will, as noted in Part 3, the Mallard that crashed in Miami in December 2005 had over 31,000 hours TIS, almost 40,000 cycles, and was 58 years old. It is an unavoidable fact that all of that “history” takes a toll.
Furthermore, in spite of the fact that Grumman had never written a “structural repair” manual for the G-73 series, the Chalk’s maintenance personnel in too many cases seem to have just made up their own repair standards as they went along instead of consulting with nominal authorities such as Frakes Aviation, the “TC Holder” for the model G-73 and for the turbine conversion (STC SA2323WE) with which it had been modified, or alternatively an FAA-approved Designated Engineering Representative (DER) or even a generic but still approved repair reference such as FAA Advisor Circular AC43.13-1B. The use of non-standard or unapproved technical references is another “red flag” in aircraft maintenance.
Equally disturbing is the fact that neither the Director of Maintenance (DOM) nor anyone else at Chalk’s seems to have had any (as the NTSB put it) “interaction” with Frakes Aviation during the 15 years leading up to the accident. Just as inconceivable, the DOM also claimed to have had no involvement with any of the comparable structural repairs on the company’s other G-73 aircraft that had been severe enough to require the services of a DER. So that begs the question – with whom at Chalk’s did the DER consult when he was called in, if not the DOM? Inadequate communication, both internally within the company and externally with OEM’s and TC Holders, and even the FAA, is another big “red flag.”
In one of the apparently all too “rare” other cases in which Chalk’s did consult a DER, another Grumman Mallard (N142PA, c/n J-42) with TIS and cycle numbers comparable to the ones for N2969 began experiencing its own seemingly critical “chronic fuel leaks” in June 2005. The DER who was hired in that case found a 22-inch crack in the right wing lower skin that was similarly hidden by the fairing between the wing and fuselage – in exactly the same area where the right wing of N2969 later failed in flight on December 19, 2005. That DER calculated that the crack in the wing of N142PA reduced its structural integrity and load-carrying capability by a factor of 50%! He testified that he told Chalk’s that the entire wing should be removed from the aircraft (no small feat!) in order to make the necessary repairs.
Chalk’s balked at such a major undertaking and chose instead to try to make all of the necessary repairs directly on the aircraft. When the entire lower skin was removed from the inboard section of the right wing so that it could be replaced, a lot of additional damage and corrosion was found on every major stringer and channel inside the wing in that same area. The DER also found evidence of numerous previous repairs that seemed to be “quite old” too.
The NTSB concluded that “on the basis of the repetitive nature of the fuel leaks on the accident airplane (N2969) and the structural damage that was found during the fuel leak inspection of another company airplane (N142PA)…Chalk’s Ocean Airways should have performed a comprehensive inspection of and maintenance on the wing structures of the airplanes in its fleet.”
With all the evidence of the extreme problems with the right wing on N142PA literally right in front of their faces, nobody at Chalk’s seems to have ever paused for as much as a moment to consider that N2969 had exactly the same fuel leak symptoms and a similar history of significant corrosion problems and structural “major repairs” in the exact same area. How much bigger of a “red flag” was necessary to get their attention?
That being said, in terms of it being a 58 year-old seaplane operating predominantly in salt water and with almost 40,000 cycles on it, the evidence strongly suggests that structural fatigue was becoming more and more of a factor in spite of whatever maintenance Chalk’s performed on it. In fact, the final NTSB report on the accident (AAR-07-04) noted that there was a significant amount of corrosion throughout the entire airframe of N2969 which resulted in “pitting and thinning” (in other words weakening) of many structural parts.
The NTSB report also noted that there was one specific area in the left wing that was so full of corrosion and stress or fatigue cracks that if the right wing had not failed when it did, the left wing was likely to have failed on its own very soon afterward. However, structural fatigue was never taken into account under the civil aviation certification requirements in effect at the time Grumman originally designed and manufactured the G-73 series in the late 1940’s and early 1950’s.
Obviously, Chalk’s maintenance and management personnel did not fully grasp or appreciate the seriousness and extent of the corrosion or the structural fatigue issues that they had with their airplanes. As already noted in Part 3, they also apparently did not grasp or appreciate the degree to which the quality of both the materials and “workmanship” used in airframe and especially wing repairs are necessary to maintain their full structural integrity when they are repaired even on the most basic level.
Beyond even that, there is a more strategic question applicable to such old aircraft with so many previous repairs all in the one problematic area; at what point do multiple repairs compromise the overall structure of the aircraft? How many “band-aids” can be put on the structure of a wing before it is necessary to completely disassemble and then fully rebuild it? The FAA (actually its predecessor, the CAA) did not require that kind of structural fatigue analysis when the Mallard was designed and certified. Probably nobody ever expected these aircraft still to be flying in commercial revenue operations almost 60 years later. By the same token, Chalk’s management seemingly failed ever to consider such factors and in so doing actually eventually pushed their airplanes past those limits.
In what can be seen as one more example of the too little, too late “blood imperative” whereby they seem to take regulatory action only in reaction to a major loss of life, less than two weeks after the crash of Chalk’s Ocean Airways Flight 101, the FAA issued Emergency Airworthiness Directive 2006-01-51 on December 30, 2005. The AD required that “before further flight… a detailed visual inspection to detect repairs, cracking, or corrosion of the wings from wing station (WS) 77L to WS 77R, front spar to rear (main) spar” had to be made. Quite unusually, it further required that any existing repairs and fuel tank sealant had to be removed as well in order to facilitate a thorough and exhaustive inspection of the critical areas.
It is noteworthy however that the initial “Emergency” version of AD 2006-01-51 acknowledged that Frakes Aviation was only then in the process of “developing special detailed (i.e. non-destructive testing) inspection procedures” applicable to the problem. Similarly, both the inspection methods and subsequent repair methods as necessary were required to be approved by “the Manager, ACO ASW-150 Rotorcraft Directorate, FAA” but similarly such methods had not yet been developed either – and so this AD effectively grounded all G-73 aircraft for a significant period of time afterward.
So, what can be done to prevent more accidents like this from occurring? Obviously, the lessons of the past must be recognized for what they are and learned by everyone involved. According to NTSB statistics, less than 20% of aircraft accidents are directly attributable to mechanical failures or maintenance issues. Still, mechanics and managers, especially in airline operations and even more so in those using seaplanes, must be able to speak and understand “seaplane” which is a bit of a different dialect than used by other aircraft. It is even more imperative that when a seaplane starts telling you it is tired or broken, or in any other way waves a “red flag” at mechanic, he must see it for what it really is and take action accordingly.
Dave Marion is the Technical Content Editor at Seaplanemagazine.com. As A&P and IA with more than 30 years of experience in aircraft maintenance, he is also a Commercial Pilot with Airplane, Single & Multi-Engine Land, and Instrument ratings. He has a BA from Colgate University in 1984 and also graduated cum laude from Embry-Riddle Aeronautical University (DAB) with a BS in Aviation Technology in 1990. He can be reached along with all of the editors via E-Mail: [email protected]