The last time the FAA grounded a commercial fleet was in 1979, after a McDonnell Douglas DC-10 crashed shortly after takeoff from Chicago's O'Hare International Airport. The suspension was reported in the June 11, 1979 issue of Aviation Week & Space Technology in an article written by future Editor-in-Chief David M. North.

DC-10 Type Certificate Lifted

FAA action follows finding of new cracks in pylon aft bulkhead forward flange; crash investigation continues

By David M. North

Suspension of the McDonnell Douglas DC-10's type certificate last week followed a separate grounding order from a federal court as government investigators were narrowing the scope of their investigation of the American Airlines DC-10 crash May 25 in Chicago (AW&ST June 4, p. 12).

The American DC-10-10, registration No. N110AA, crashed shortly after takeoff from Chicago's O'Hare International Airport, killing 259 passengers, 13 crewmembers and three persons on the ground. The 275 fatalities make the crash the worst in U.S. history.

The controversies surrounding the grounding of the entire U.S. DC-10 fleet and, by extension, many of the DC-10s operated by foreign carriers, by Federal Aviation Administrator Langhorne Bond on the morning of June 6 to revolve around several issues.

The first issue involves the grounding of all DC-10 models, when most of the problems being found in the aft pylon area have been attributed by the FAA primarily to the DC-10-10. The second issue, and the most critical in terms of how much time it will take U.S. airlines, McDonnell Douglas, the National Transportation Safety Board and the FAA to get the DC-10s flying again, is the cause of cracks being found in the forward flange of the DC-10s pylon aft bulkhead.

A further issue is likely to erupt among detractors of the FAA as to why the agency did not ground the aircraft immediately after a U.S. district court judge issued a temporary restraining order grounding the aircraft on June 5.

The first issue, that of the FAA suspending the type certificate of all DC-10 series aircraft, brought an angry response from McDonnell Douglas.

One company official said: "We are making every effort to assure a prompt return to service of the DC-10, and will take whatever steps are necessary to accomplish that goal. Today's FAA action is more sweeping and drastic than circumstances warrant because the pylon aft bulkhead cracks found during inspections have all been on DC-10-10 aircraft, because they have involved aircraft that may have suffered from maintenance procedures at variance with the manufacturer's recommendations and because no such cracks have been found on DC-10-30 or DC-10-40 aircraft."

When asked last week why he was grounding all DC-10s, Bond responded that the DC-10 series aircraft had "sufficient design commonality to raise suspicions," and that he would rather "err on the side of safety" in the grounding of all series of aircraft.

As to why he was now suspending the certificate of the DC-10, when earlier he grounded the aircraft and then released it for flight, Bond answered that he had gone from a "certitude of a high likelihood of no risk to a sufficient likelihood of risk."

The emergency order of suspension for DC-10s not only grounded the 138 U.S.-registered aircraft, but also most foreign-registered aircraft. Those countries having bilateral agreements with the U.S. covering aircraft certification were required under the agreement to ground the DC-10s registered in their country. Those countries not included in bilateral agreements were being notified by the FAA last week that the DC-10s operated under their registration could not fly into a U.S. airport or use U.S. airspace. Foreign countries were being told that they could ferry their aircraft to their home maintenance bases.

An American Airlines DC-10 crashed after its No. 1 engine broke loose on takeoff from Chicago's O'Hare International Airport on May 25, 1979. A faulty maintenance procedure was ultimately blamed for the incident, which claimed the lives of all 272 people aboard the aircraft and three on the ground.

The suspension order grounded all DC-10s immediately, with domestic airlines not allowed to ferry their aircraft. Meetings were being held at FAA headquarters on June 6 to determine a procedure that would enable U.S. carriers to ferry their DC-10s to their maintenance bases.

Bond and the FAA base their suspension of the type certificate of the DC-10 on two cracks found in the aft bulkhead forward flange of two American Airlines DC-10s in San Francisco on the evening of June 5 and to possible gaps in the original fail safe certification analysis. The cracks had not been located during earlier inspections, which raises the question of whether the cracks had been there during the earlier visual inspections and not seen, or whether the cracks, found in this case by dye penetrant inspections, were new ones. The answer to these questions will determine the procedure the FAA will have to use to restore the DC-10's type certificate.

The initial response of the safety board in finding a fractured forward thrust link attach bolt at the accident site was to suspect this bolt as a possible cause of the DC-10 accident. The FAA issued an airworthiness directive on May 28 ordering that the bolts be inspected or replaced and that the forward flange of each wing engine pylon aft bulkhead be inspected for cracks.

Subsequent inspections of the DC-10 fleet revealed further cracks in the wing pylon area, which prompted a supplementary airworthiness directive by the FAA on May 29, grounding the aircraft until the required inspections were completed. The supplementary directive required operators to conduct a visual inspection of the entire remaining pylon-to-wing attach area not covered by the original directive.

On May 31, a safety board official said the crack in the pylon forward thrust link attach bolt was not due to fatigue, but to stress, which fractured the bolt.

Emphasis Switched

At the same time the emphasis of the investigation was switching to the possibility that cracks in the pylon's aft bulkhead forward flange could be the main problem in the pylon-to-wing attachment. The cracks were being attributed by the safety board to maintenance procedures used by American Airlines and some others in removing and reinstalling the pylon with the engine attached.

In its recommendation to the FAA on June 4, the safety board said:

"While complying with the FAA's initial airworthiness directive requiring inspection of the engine pylon mounting structure of DC-10 aircraft, American Airlines found two aircraft in their fleet, N106AA and N119AA, with damage to the pylon aft bulkhead. The aft bulkhead is the structural element that contains the spherical bearing that carries the aft attachment of the pylon to a mating clevis on the wing structure. This fitting provides the major reaction to vertical and side loads imposed on the pylon.

Physical Impact

"The damage observed on both N106AA and N119AA was a crack in the center of the horizontal upper flange directly beneath the attachment bearing. The crack on N106AA was reportedly 2 in. long and the crack on N119A was reportedly 5 in. long. When inspected visually, it was apparent that the crack on N106AA was caused by physical impact. Further investigation disclosed that this impact probably occurred when the pylon was installed during previous maintenance.

"American Airlines had begun a program last fall to comply with Douglas Aircraft Co. service bulletins 54-48 and 54-49 when the aircraft were undergoing periodic checks at their maintenance facility in Tulsa, Okla. This maintenance was performed on N106AA on Dec. 7, 1978, and on N119AA on Mar. 19, 1979."

The safety board recommendation to the FAA also said: "Compliance with these service bulletins requires that the pylon be lowered from the wing structure for the installation of new bearings in the forward and aft bulkhead fittings. American Airlines procedures for removing and reinstalling the pylon consisted of lowering and raising the pylon with the engine still attached, by supporting the entire assembly by a forklift placed under the engine.

"Board personnel who observed this procedure noted that the forklift operator had limited control in the precise placement of the aft bulkhead fitting into the wing-mounted clevis during reinstallation of the pylon. Vertical misalignment of a fraction of an inch can result in the pylon aft bulkhead upper horizontal flange assembly striking the forward ear of the wing-mounted clevis, causing the flange to crack.

"The board believes that this occurred on both N106AA and N119AA. The installation geometry of the pylon aft bulkhead and the lower wing structure is such that an inspector cannot observe the crack easily. Thus, any damage which has occurred as a result of the installation process procedure is likely to be undetected."

More specifically on the DC-10 accident, the safety board's recommendation to the FAA said: "While the investigation of the accident involving N110AA is continuing, preliminary evidence indicates that the forward flange on the No. 1 pylon aft bulkhead fitting had failed completely. Metallurgical examination disclosed that there was a preexisting crack about 10 in. long in the same area where cracks were evident on the other two aircraft. N110AA had been subjected to the engine removal and reinstallation procedure on Mar. 30, 1979. The aircraft had accrued 430 flight hours since that time."

Although the Douglas service bulletin specifies removal of the engine before reinstallation of the pylon to wing attachment fittings, the safety board is aware that several operators are using the same procedure as American Airlines.

In the June 4 recommendation, the NTSB asked the FAA to issue a telegraphic airworthiness directive requiring an immediate inspection of all DC-10 aircraft in which an engine pylon assembly has been removed and reinstalled during the recent inspections and another recommendation that the practice of lowering the pylon with the engine attached be discontinued by the DC-10 operators.

'Gratuitous and Unnecessary'

In response to the claims by McDonnell Douglas that airlines are using maintenance procedures not authorized by the manufacturer, which also could be applicable to the safety board's claims that American Airlines did not follow McDonnell Douglas service bulletins, American said last week that McDonnell Douglas charges were "gratuitous and unnecessary."

Donald J. Lloyd-Jones, American's senior vice president for operations, said engine and pylon installations are performed by other U.S. airlines in the same manner followed by American. He added that two representatives of the McDonnell Douglas product support department were present when American changed its first DC-10 pylon on Apr. 17, 1977, in Los Angeles and at another change 10 days later.

"McDonnell Douglas representatives have been present on subsequent occasions when pylon changes have been made," Lloyd-Jones said. "Our people are skilled in the procedure, and we have no reason at all to believe that it is in any way responsible for the defects that our rigorous inspections have uncovered.

"We are perplexed and disturbed that McDonnell Douglas has taken aim at an industry procedure that it has been aware of, has participated in and never objected to."

Following the June 4 safety board recommendation, the FAA on the morning of June 5 issued on its second supplement to its original airworthiness directive. The supplementary directive said:

"Reports have been received that some DC-10 operators have removed and reinstalled engines and pylons as an assembly. It has been observed that in reinstallation of the pylon assembly, the aft bulkhead forward flange can be damaged by impact with the pylon aft support fitting."

The supplement was directed at those operators who had used the pylon and engine assembly procedure, and required they perform a new inspection of the pylon aft bulkhead and reinstall the pylon and engine separately prior to further revenue flight. The directive was believed by FAA to be applicable to six DC-10s, four of U.S. registry and two foreign registered.

Early last week, the FAA was receiving the tally of the problems found on U.S. registered DC-10s, required in its original directive and the supplementary directive. The total was 59 items that were applicable to the general area of the pylon-to-wing attachment. These items included:

* Loose bolt web structure -- 18 items.
* Thrust link bushings -- 8.
* Monoball bolt loose -- 5.
* Monoball cracked -- 5.
* Huck bolt sheared -- 4.
* Rear mount cracks -- 3.
* Cracked pylon structure -- 3.

The next event in the forthcoming grounding of the DC-10s occurred on June 5 when the legal counsel of the Airline Passengers Assn. filed for a temporary restraining order against the FAA in the U.S. District Court for the District of Columbia. The judge issued the temporary restraining order at 4:45 p.m., and at approximately 9:00 p.m. on June 5, he issued a stay on the order until the next morning so that FAA counsel could gather its evidence to present to the court to stop the order.

According to one FAA official, between 9 and 11 p.m. on June 5, American Airlines found two cracks in two pylons' aft bulkhead forward flanges by using a dye penetrant test in the 100-hr. check required by the earlier FAA directives.

"What scared us was that these two aircraft did not come under the final supplementary directive covering those aircraft that had their pylons and engines removed as one unit during earlier inspections," he said. "This would lead us to believe that unless they were missed in the earlier inspections, they are new cracks, and the maintenance procedure reason for the cracks will not hold up.

In the emergency order of suspension, the FAA said:

"Moreover, the preliminary findings of an FAA post audit of the model DC-10 aircraft type certification data indicate that the wing pylon assembly may not comply with the type certification basis set forth in FAR 25.571."

"What that means," the FAA official said, is that in the original certification data, the "pylon's aft bulkhead forward flange was not considered to be a problem area, so that it either was not included in the fail safe analysis or we do not have enough data on the original analysis."

It was this realization plus the two cracks that prompted FAA's Bond to ground the DC-10s and return from a London meeting on June 6 for a press conference the same day.

The FAA's dilemma and Bond's is that if the cracks found in the American Airline's DC-10s are new since the last inspection, there could ensue a long process of design change and fail safe analysis. If it is discovered that possibly the cracks had been in the pylon during the earlier visual inspections and not caught until the more thorough dye penetrant inspection, the FAA's solution could be faster and limited to fewer aircraft.

Length of Grounding

During his press conference, Bond could not be pinned down by repeated questions directed at how long the grounding was to last. Also, in response to questions regarding the court's temporary restraining order, which was finally imposed against the FAA and the DC-10 on June 6, Bond said that the agency's grounding was independent of the court's actions.

The Airline Passengers Assn. counsel disagreed, saying: "We do not think that the FAA would have grounded the DC-10 if it had not been for the temporary restraining order."

Concerning the other wide-body transport aircraft, the FAA is forming a special certification review team that will evaluate the wide-body manufacturers' and operators' compliance with all applicable directives on the engine-to-pylon-to-wing attachments. The agency also is drafting directives that would require inspection of the other wide-body pylons.