Dear Mr. Caldwell,
Please accept the following both (a) as my requests for timely information before the comment period expires on October 7, 2009, and (b) my preliminary comments on subject Airworthiness Concern Sheet. On September 14th at 01:21 CDT I emailed you three separate questions about subject Airworthiness Concern Sheet (hereinafter referred to as ACS) but, to date, have received no response.
To such extent as the FAA does not timely provide such information identified herein as missing (and deemed pertinent to revealing and understanding precisely what progression of events lead to "the in-flight breakup of an Ercoupe Model 415-D..."), each hereinafter designated "IR" (Information Request) followed by a reference number, please accept these preliminary comments as final comments if or when the statutory period for submission of comments expires (which presently appears to be 10/07/09).
With reference to the listing of comments solicited, or "encouraged" by the FAA:
It is not presently possible to make specific comments either for or against 09.087 because that document has not been specifically attached to this ACS. If a listing of current or pending FAA "safety recommendations" exists online, I have been unsuccessful in locating or accessing same. If it can be downloaded on the web from the FAA site no link or directions for such download have been provided. This is but one of numerous good reasons to revise and reissue this ACS with the missing information with a new "response date" allowing reasonable review of said missing information and an appropriate comment period. Please consider this informational deficiency as IR#1.
It also seems inappropriate for the FAA to issue an "airworthiness concern" originating as speculation in a preliminary accident report which is subject to change when no final decision has yet to been reached by the NTSB as to the actual or most likely cause of said accident. The AD process should not be initiated without clear and certain cause. If the 09.087 author and his/her title is not apparent on the reproduced document, such information is hereby requested as IR #2.
If 09.087 urges the FAA to revise AD 2003-221-01 "requiring a complete wing spar inspection for corrosion, damage, and any unauthorized maintenance actions performed on the wings of all Univair Models", such general terminology would also include aircraft formerly manufactured by Stinson. If an ACS has been generated for such models, please consider this my request for a photocopy of same as IR#3.
It is not apparent whether the "FAA Description of Airworthiness Concern" is taken verbatim from 09.087. It would appear to incorporate information from the NTSB preliminary Accident Report, statements of witnesses, reports of accident investigators and engineers who performed the metallurgy analysis of the failed spar. Inasmuch as inaccuracies could result if accident investigators further interpret the written findings of metallurgy analysis by engineers, please consider consider this my request for a photocopy of the complete and signed engineering metallurgy analysis as IR#4.
The "unsafe condition" presently described in AD 2003-21-01 is "...to prevent wing damage caused by a corroded wing outer panel structural component, which, if not detected and corrected, could progress to the point of failure." If similar wording were used in a new AD based on this ACS, it would likely read "...to prevent such in-flight wing failure(s) in the fuselage center section of the wing spar as might originate from one or more holes therein."
Since each "unsafe condition" is clearly different as to origin and location, why does 09.087 apparently urge amendment to an existing and different AD? The cost burden of such a regulatory hermaphrodite would clearly be of greater repetitive burden to owners and no discernible increase in safety. In this regard I must ask, as my IR#5, if it easier and/or quicker for the FAA to modify an existing AD than to issue a new one; and, if so, precisely how and why.
Any genuine concern that this single accident has uncovered a genuine fleet-wide safety problem in Ercoupes should be supported by considerable credible evidence. The load carrying capability of no spar in no airframe is further compromised by an "unauthorized" hole" as opposed to one fully and properly authorized. As my IR#6 please explain why the airworthiness of spar in a given operational aircraft is in any manner less safe simply because one owner or mechanic succeeded in properly documenting same in official aircraft files and another did not.
If the role of the FAA in "interstate commerce" is to establish and enforce standards of design and safety that properly balance common sense and reasonable cost, however subjective those terms may be, it must not inadvertently, arbitrarily or unreasonably expand its authority in any manner as would have contrary effect. To greatly oversimplify an obvious truth, every spar has a limit of stress beyond which it will break. But in terms of safe flight it would be inappropriate to consider spar strength in the abstract as this ACS appears to do.
CAR 04 and the Normal category design requirements therein as to the overall loads the wing structure must be designed and maintained to carry. So long as a hole in a spar, whether "authorized" or "unauthorized", cannot be shown to reduce the load bearing capability of a given operational airframe operated in the Normal category below that required by CAR 04 no "unsafe condition" has been shown to exist.
In the absence of such "unsafe condition" the FAA has no authorization or mandate to inspect or "remedy" anything. In this context I ask the FAA to explain why the open-ended terminology of "unauthorized maintenance" has been utilized without any showing whatsoever that such "unauthorized maintenance" was an actual or materially contributing cause of this accident. No evidence whatsoever has been presented that "unauthorized maintenance" of any type represents a greater danger to the safety or continuing airworthiness of the Ercoupe fleet than other aircraft designs. If evidence to the contrary exists, I would ask for that as my IR#7.
A parallel example would be the failure of a metal propeller at a point of leading edge damage by foreign objects. Such damage is "unauthorized", but common in the field. The administrator has investigated and disseminated criteria for mechanics to inspect such propellers periodically and identify with reasonable certainty such damage as would make the propeller no longer airworthy versus that which can be repaired in accordance with procedures deemed acceptable to the administrator and the propeller then returned to service.
Mechanics drill holes every day in airframes without owner consultation. They are trained and certificated in proper techniques and most owners trust them implicitly, whether such trust be warranted or not. If there be legitimate basis for bringing into regulatory question the airworthiness of an operational airframe simply because a hole may be found to exist somewhere in it that is undocumented in aircraft records and/or considered "unapproved", that information is conspicuously absent. If such exists, I would ask for that as my IR#8.
To such extent as a hole in a spar could represent a genuine "airworthiness concern", such concern would not be unique to Ercoupes and should not be addressed by an AD limited to Ercoupes. In actual fact, Ercoupes have a far deeper and stronger spar than almost any other light plane design. To such extent as this accident resulted from a sequential and progressive catastrophic overload, such ultimate failure where one or more holes were drilled is merely incidental and certainly not causative. Any belief by anyone that certain "suspect" holes in the spar caused the structural failure preceding these two fatalities presumes facts not in evidence. If such facts exist as would support such speculation, I would ask that these be provided as my IR#9.
A competent engineering analysis should have attempted to evaluate whether or not the center section spar failed after being subjected to in-flight stress in excess of design requirements. It should include examination of the outer sections so as to determine, insofar as is possible, control system play and whether failure of the wing tip structure on one or both sides or other outer panel failure precipitated subsequent center section spar failures. My IR#10 is: was this done, and, if not, why not?
It seems almost inconceivable that no mention was made as to the presence or absence of aileron counterweights on the accident aircraft, and whether or not that presence or absence was consistent with official aircraft records. Ercoupe Service Memorandums 56 and 57 describe acceptable aileron play as 7/16" at the trailing edge with the weights and 5/16" and recommend removal and subsequent inspection of play at 100 hr. intervals. There is no mention of any NTSB attempt to ascertain whether or not excessive play was present in the aircraft aileron system at the time of this accident, although structural failure of certain control pushrods was both observed and noted.
Two thirds of our overall fleet was manufactured in a one year period from the fall of 1945 thru the fall of 1946. Over one third of the overall fleet remain on the FAA "active" register. Only a tiny percentage of such total aircraft produced have suffered in-flight breakup from all causes. We are left to speculate as to how many resulted from known or likely flights into instrument conditions by persons unqualified, how many from the undue stress of unauthorized aerobatics, or how many from substandard maintenance practices.
Unless and until the Ercoupe design is shown to be more prone to such structural failure than other operational approved designs there is no reasonable basis for questioning the overall safety of the Ercoupe fleet at this time. Over fifty years comprised of literally countless flights ending safely should establish beyond reasonable doubt that such failure in a typical airframe as typically operated and maintained has been, and will continue to be, extremely rare. No valid purpose is served by disproportionate concern over a single failure so rare as to have no statistical significance.
There is ample evidence that virtually identical catastrophic in-flight structural failures have occurred before without arousing such official speculation as this ACS. The likely reasons are that the ERCO factory and its knowledgeable personnel no longer exist for consult, and FAA personnel of today lack the technical familiarity with Ercoupes common among CAA professionals when Ercoupe were considered "state of the art" low wing monoplanes. I shall try to bridge some of this gap with historical information from my files:
a. A Form ACA-1226 "Malfunctioning And Defects Report" was submitted 1/30/48 by an Ercoupe owner describing a flight on 1/25/48 thusly: "Intended doing a slow roll to the left and at the outset exceeded the placarded safe speed of the aircraft and at the halfway point of the maneuver used forward pressure on controls due to the nose being low. At this point there occurred a loud "Pop" and apparent structural damage took place at that instant. Excessively violent vibration followed until full recovery was made." As to the "probable cause and recommendations to prevent recurrence" the owner responded "Excessive speed plus the maneuver. D O N'T !!!"
A photocopy of this document in Univair's ERCO files will be forwarded with the hard copy of this response as Attachment #1 by U.S.P.S. Certified Mail.
b. On November 8, 1948, Bob Sanders of Sanders Aviation issued "Ercoupe Take-Offs" #G3 entitled "Discouraging Aerobatics". This describes instances of "wing tip failures" and other structural failures reported in "recent months" and that "...we were not surprised or alarmed since evidence presented strongly indicates misuse of the Ercoupes involved." He explains that the 144 mph red line "indicates the maximum speed for which the airplane is designed", pointing that all airplanes have a similar restriction and that speeds above this "will endanger the airplane and occupants inasmuch as excessive speed may induce wing flutter or other unpredictable difficulties which will, in some cases, cause immediate collapse of the structure". We have all seen reports of difficulties of other popular make airplanes caused by pilots exceeding design limitations." His last paragraph urges dealers to cooperate "in bringing to the attention of all Ercoupe owners and pilots the seriousness of exceeding the air speed red line and the inadvisability of doing aerobatics in the airplane since they may easily exceed the speed or accelerations which can be safely borne by the structure."
A photocopy of this document in Univair's ERCO files will be forwarded with the hard copy of this response as Attachment #2 by U.S.P.S. Certified Mail.
c. On December 1, 1948, W. L. Greene, then Chief Engineer of ERCO, wrote the CAA Aircraft Components Branch, Airframe & Appliance Engineering Division (1-301) following "several airplane accidents involving wing failure in flight". He states that "We are of the opinion that the most probable cause...is aileron flutter caused by a loose aileron control system. The wreckage of these airplanes...all indicated...failure of the main wing spar was caused by a negative lift load on the wing tip. This load could be applied in normal flight on a smooth day by a substantial twisting of the wing to provide a negative angle of attack of the tip. It...appears that a violent distortion of the wing took place from some cause. The only obvious cause appears to be wing tip or aileron flutter." In test flights investigating wing flutter, and with 9/16" looseness in the control system "we obtained a violent wing flutter, or aileron flutter, which caused the right aileron to be torn from the hinge attachments and leave the airplane at a speed of about 190 miles an hour...". He concluded by saying that "shortly after the accident in Illinois, we indicated that the report...was incomplete and we would like to have a more thorough inspection of the airplane, which we understood was still flying" because "such information might help us in further evaluating this and the other accidents similar to it in which the pilot did not survive." Ercoupe Service Memorandum No. 56, of December, 1948, was issued immediately following this correspondence.
A photocopy of this document in Univair's ERCO files will be forwarded with the hard copy of this response as Attachment #3 by U.S.P.S. Certified Mail.
d. On April 20, 1950, Norman A. Hubbard, D.E.R. 1-21 for ERCO wrote the CAA, Attn.: Chief, Aircraft Division (1-565) relative to flight tests for C.A.A. approval of the installation of the Trim-o-matic in Models E and G only. He mentions "The recent accident during flight test of the Trim-o-matic installation...occurred at about 180 mph calibrated air speed." The next week, on April 27, 1950, Bob Sanders of Sanders Aviation issued "Ercoupe Take-Offs" #P-7 entitled "TEST FLIGHT--1950 Ercoupe". This describe the decision "to dive the airplane to the higher speed...required to approve the...installation on earlier airplanes, which were not limited against aerobatic maneuvers. In the process of this dive, which went to 185 m.p.h., something happened to the airplane causing it to nose down sharply, throwing me out of the airplane and causing substantial damage to the airplane, which resulted in its disintegration. ...initial and unofficial opinion is that the nose ribs of the outer panels deflected, initiating the failure. The rapidity with which I was thrown out, without any advance warning of failure...impels me to again...discourage aerobatics which may encourage unskilled pilots to get into speed ranges and attitudes which are dangerous to them and their airplanes."
Photocopies of these documents in Univair's ERCO files will be forwarded with the hard copy of this response as Attachments #4 and #5 by U.S.P.S. Certified Mail.
The ACS description of the "improper maintenance" performed on the wing spar, "holes drilled into wing spar to facilitate remounting of a seat pan and other unauthorized components", is so vague as to be meaningless. Where these holes were drilled? How many? What size? Where are the engineering calculations that would suggest that holes of this size, number, and arrangement at this location would reduce the structural capacity of the assembled wing (not just the spar) to a value below design requirements applicable to a light aircraft for the "normal category? Where, precisely, did the wing spar fail? Please consider these questions my IR#11.
Were surviving records or logs of said aircraft reviewed in detail so as to determine when, or approximately when, subject "improper maintenance" was accomplished? It would be of significance if the aircraft continued to operate safely for a period of years and/or significant flight hours from the "unauthorized maintenance" until the fatal flight. Please consider this question my IR#12.
Was a diligent effort made to ascertain when the accident aircraft was last fueled before the accident flight and whether its tanks were filled at that time? This, together with the actual or estimated weight of the occupants and estimated fuel consumption in flight would facilitate a reasonable estimate as to likely aircraft weight at the time of the accident. Please consider my request for any and all such information as my IR#13.
I have learned from the NTSB preliminary accident report that the accident airframe was N99154, and my files show this to be Serial Number 1777 manufactured 6/3/46. This airframe was originally manufactured as a 415-C. Do the maintenance records indicate conversion to model 415-D specification in accordance with Ercoupe Information Letter No.1 dated January 1, 1956? What was that date and what was the time on the airframe? At the time of the accident, did it retain the original bench seating? Was there evidence that bucket seats were or had ever been fitted and, if so, when (in terms of both calendar date and airframe time). Please consider this question my IR#14.
Without original 415-C production drawings, information and dimensions as to the original bench style 415 series Ercoupe forward "seat pan" mounting attachments and hardware are not known. Please research and provide the location, number, arrangement and size of such holes so owners may thus identify such additional holes and/or oversized holes as may be "unauthorized" on active aircraft. Please consider this question my IR#15.
The "Trim-O-Matic" lateral trim adjustment was incorporated into the Mode 415-G for 1950. It was approved for retrofit into earlier models as SK-20 and necessary holes for installation are described in Ercoupe Service Memorandum No. 54 of July 25, 1950; and more specifically depicted on drawing 415-52175, Change "A". While I do not have a copy of said drawing, it should be in CAA/FAA Ercoupe files. This production change received appropriate FAA review, was timely approved over fifty years ago, and has proven safe in extended service. Accordingly, there should be a strong presumption that any associated reduction in spar strength is of no overall structural significance. Please research and provide the location, number, arrangement and size of related holes so owners may thus identify such additional holes and/or oversized holes as may be "unauthorized" on active aircraft. Please consider this question my IR#16.
Per production drawing F53180 (Rev. B dated 6/10/60), the Forney F-1A bucket seats are secured at the front by one left and right hook mounts of similar construction. Centerlines of these hooks are 4.437" outboard of the aircraft centerline and then 10" further outboard on each side. Each such hook is mounted to the main spar by four 8-32 fasteners. Installation required a total of sixteen 11/65" (.171) holes to be drilled through the spar cap. These are drilled in pairs, aligned fore and aft, at eight locations. Per production drawing F53189 L/R (Rev. A dated 2/4/60) the fore-aft separation is .875". Per production drawing F53190 L/R (Rev. A dated 2/4/60) the port-starboard separation is 1.468".
Holes drilled in the main spar for the forward attachment of bucket seats installed in later production Forney, Alon and M10 (TCDS 787) airframes may or may not be identical in number, size and location between manufacturers. Please research and advise as to any variations, considering this request my IR#17. The production change to bucket seats received appropriate FAA review, was timely approved almost fifty years ago, and has proven safe in extended service, and has been approved as a retrofit in earlier airframes by approved 337. Accordingly, there should be a strong presumption that any associated reduction in spar strength resulting from the drilling or presence of such holes is of no overall structural significance.
The Forney F-1A and later models mounted their Trim control on the main spar. The pattern of associated mounting holes is not known. This production change received appropriate FAA review, was timely approved almost fifty years ago, and has proven safe in extended service. Accordingly, there should be a strong presumption that any associated reduction in spar strength resulting from the drilling or presence of such holes is of no overall structural significance. Please research and provide the location, number, arrangement and size of related holes so owners may thus identify such additional holes and/or oversized holes as may be "unauthorized" on active aircraft. Please consider this question my IR#18.
If the above trim system were installed in an earlier airframe without bucket seats, the method of mounting may be different as to holes drilled in the spar. There should be a strong presumption that any associated reduction in spar strength resulting from the drilling or presence of such holes is of no overall structural significance unless the location, size, number and/or arrangement of such holes is shown to be so materially different from those previously reviewed and approved so as to result in a reduction of the overall structural capacity of the assembled wing to some value less than that required by applicable normal category design criteria.
In consideration of any and all spar holes drilled for installations described above, it would seem that there should be a strong presumption that any associated reduction in spar strength resulting from the drilling or presence of "unapproved maintenance" holes is of no overall structural significance unless the location, size, number and/or arrangement of such holes can be shown to be so materially different from those previously reviewed and approved as to reduce the overall structural capacity of the assembled wing to some value less than that required by applicable Normal category design criteria.
In conclusion, none of the information comprising this ARC credibly supports the unfounded speculation that "unapproved maintenance" holes were the primary reason that this structural failure occurred. To the contrary, information available now suggests that the airframe of the accident Ercoupe was subjected to in-flight stresses in excess of applicable design standards; with subsequent structural failure being, at some point, eminently predictable and wholly inevitable.
This has happened before and it is unfortunately likely that it will happen. Catastrophic in-flight structural failures in general are not unique to Ercoupes, therefore an AD addressing such non-specific threat pertaining solely to Ercoupes is simply not warranted. It would have absolutely no effect in preventing substantially identical catastrophic in-flight structural failures in the future.
On the other hand, issuance of a new AD mandating yearly compliance with Ercoupe Service Bulletins 56 and 57 yearly and again cautioning operators of the dangers of aileron flutter and exceeding the aircraft red line speed might very well reduce the frequency with which future catastrophic in-flight structural failures in Ercoupes and later variations originate from substandard maintenance practices.
Sincerely, William R. Bayne .____|-(o)-|____. (Copyright 2009)
