For the second time in recent months, calls for required safety actions have resulted in advisory, not required, responses. The most recent case involves a bulletin issued March 3 by the Federal Aviation Administration (FAA) on maintenance record-keeping for horizontal stabilizer jackscrews on Douglas-built DC-9/MD-80/90 series airplanes and on the Boeing [BA] B717, a derivative model of the Douglas series (see ASW, April 19).
The document in question is Flight Standards Information Bulletin for Airworthiness (FSAW) No. 04-03. It is an outgrowth of the fatal January 2000 crash of an Alaska Airlines [ALK] MD-83. The threads on the jackscrew recovered from the wreckage had been nearly completely stripped, and in the course of its inquiry National Transportation Safety Board (NTSB) investigators uncovered egregious shortcomings in maintenance and maintenance record-keeping (see ASW, Jan. 1, 2001). Among the numerous recommendations coming out of the investigation, NTSB Recommendation Number A-02-46 said the FAA should “require” maintenance facilities that overhaul jackscrews to record and inform customers of the end play measurements.”
The FSAW specifically mentions that it is being published in response to this recommendation. However, numerous sources point out that an FSAW does not require compliance, as would be the case with an airworthiness directive (AD).
Rather, this FSAW ostensibly provides guidance for primary maintenance inspectors (PMIs) to do their job, while giving maintenance facilities and operators a heads-up on what is expected of them for maintenance record-keeping.
The bulletin calls for jackscrew end play measurements to be recorded whenever the assemblies are overhauled. If the end play is at 0.040 inch, the assembly, a mated acme nut and acme screw, must be replaced. The FSAW calls for final fits and clearances to be recorded, and enjoins FAA PMIs to make sure the work is recorded in the agency’s program tracking and reporting subsystem (PTRS). Moreover, if a contractor overhauls the jackscrew, the airplane operator should be provided the end play measure. The rationale outlined in the FSAW is as follows:
“It allows the operators to record end play measurements for the same assembly after it is installed on an airplane. This allows a cross-check of verification of the installed measurement, which is used to ensure the jackscrew assembly will not exceed the maximum wear limit before the next scheduled end play measurement.”
What the FSAW does not say is if the end play measurement is 0.039 inch, how much life remains? How much time exists before the assembly must be replaced? According to Boeing, the acme nut threads were designed to wear at a rate of 0.001 inch per 1,000 flight hours. Thus, when the jackscrew end play was first measured when the Alaska accident airplane was undergoing heavy maintenance in 1997, the end play measured 0.040. As such, replacement was required. At that time, the airplane had 17,700 flight hours. Because of the haste to return the airplane to revenue service, the end play was rechecked and came in at 0.033 inches. As such, it had about another 7,000 flight hours of service. Three years later, the threads failed at 26,600 flight hours – nearly 9,000 hours of additional service. The point is that wear limit is significantly affected by wear rate, about which the FSAW is silent.
To ASW contributing editor John Sampson of the International Aviation Safety Association (IASA), the FSAW lacks clout. “Divorcing the desired record-keeping from a legal document – an AD – and just making it a PTRS step does not shine through as a determined effort,” he opined. He went further, characterizing the FSAW as a “reverse Midas touch,” turning gold into lead, the gold being the NTSB recommendation and the FSAW’s dilution of “required” into advisory “lead,” as it were.
Sampson’s recollection of the revelations following the Alaska crash summarize the background and meaning of the FSAW:
“Prior to Alaska’s crash, there was nil coordinated overhaul and inspection intervals (or even re-greasing) for DC-9/MD-80/B717 class airplanes sporting this jackscrew design. The intervals varied extremely over various operators. The greases and mixes of greases also were a bone of contention. Micrometer screw gauges used to measure end play had not been calibrated. Records were lousy. Individual technicians’ identities were unclear. ATOS [the FAA’s Air Transportation Oversight System] was exposed as a sham.
“It is not rocket science to deduce that, once worn to limits, nominal wear rates are ‘out the window’ and real-life wear rates are going to eventually go exponential. Fatigue management has become a science, but it would appear that initiatives for wear management are either stillborn or worn out.
“I see the FSAW as more like a service bulletin – one that is not issued by the manufacturer, but by the FAA – in an attempt to informally put the matter, and future servicing records, into some semblance of order.”
The record-keeping could have been pushed considerably further. Paragraph 6 of the FSAW outlines the items that should be included in the jackscrew assembly overhaul records. The missing chord from this tune is any mention of maintaining physical evidence of the work. For example, a digital photograph could (should?) be taken of any flight-control critical items where tolerances are involved, such as the end play of the jackscrew. Any near-to-limits item could be photographed from two different (stereoscopic) angles while clutched in the jaws of a micrometer screw-gauge. As an adjunct, the identifying serial number of the screw gauge could be photographed. If this approach sounds extreme, note that dentists nowadays routinely employ X-rays and digital photography to secure themselves against any later legal reprisal. And human teeth, one should note, are not life-critical, as are some metal gear teeth on airplanes.
The view that the FSAW falls short is shared by Paul van Eenige, airworthiness information officer for the Civil Aviation Authority of The Netherlands (CAA-NL). “The FSAW leaves me with the impression that the problem may have been addressed but not necessarily solved,” he told ASW. Van Eenige pointed out that he was speaking for himself, not stating any official views of the CAA-NL.
“The relevant AD 2000-15-15 is much clearer, although it does not contain any requirements for record-keeping,” he added. Van Eenige was referring to the AD issued Aug. 23, 2000, requiring operators to inspect the jackscrews on their planes for metal shavings and flakes, which could lead to excessive wear.
Van Eenige suggested revising this important AD to include the “guidance” contained in the FSAW. Van Eenige based his argument on three points:
1. Unless they read ASW, European airlines are not likely to be aware of the FSAW. Moreover, van Eenige added, “Several European authorities have followed the FAA’s example by issuing documents like ‘Recommended Bulletins’ or something with a similar title. It is not clear whether anyone in the industry, either the airlines or general aviation, actually does much with these.”
“As far as I know, there are currently no agreements in Europe among the authorities – or a European Aviation Safety Agency (EASA) position – on how to handle such documents,” he said.
2. On the other hand, EASA has declared that ADs issued by third countries will apply to aircraft registered in European Union (EU) member states. However, this EASA mandate does not include such documents as an FSAW.
3. As a result, European airlines or maintenance companies may not be required to adopt all NTSB recommendations or adopt measures taken by the FAA to address “unsafe conditions” unless some other “status” for documents like FSAWs is decided upon. Presently, the only document with such regulatory and Trans-Atlantic “standing” is an AD.
“There needs to be some discussion of this subject, as harmonization across the Atlantic is very important,” van Eenige declared.
Second time now
FSAW 04-03 is the second non-mandatory document issued recently by the FAA in response to NTSB recommendations for “required” action. On Aug. 18, 2003, the NTSB called for “required” compliance with manufacturer service bulletins (SBs) regarding the F-800 digital flight data recorder (DFDR). In response, on Dec. 2, 2003, the FAA issued special airworthiness information bulletin (SAIB) No. CE-04-24 urging operators to adhere to the SBs. As in the case of FSAWs, SAIBs are not mandatory. In fact, the words “Recommendations aren’t mandatory” appear at the top of every SAIB. Yet in other instances of dubious DFDR functional reliability, the FAA issued ADs mandating SB compliance (see ASW, Jan. 19).
The plethora of non-binding documents suggests a regulatory “twilight zone” and the need for more consistent policy, especially in those cases where the NTSB is seeking “required” as opposed to “advisory” or “informational” action. For example, the NTSB recommended the publication of an advisory circular (AC) on in-flight firefighting, and the FAA responded accordingly (see ASW, April 12). >> Van Eenige, e-mail [email protected] <<
The Jackscrew Overhaul Record Should Include:
- The date the work was performed.
- A detailed description of the work performed.
- A listing of the final fits and clearances.
- A detailed description of the overhaul testing and the results thereof.
- The technical data used to conduct the testing.
- The identity of the person who performed the work.
Source: FSAW 04-03, par. 6
Wear vs. Flight Hours
The wear rate on the jackscrew installed in the Alaska Airlines accident airplane actually was greater than the nominal 0.001 inch per 1,000 flight hours, as shown by the circle at the 1997 overhaul point marking the first end play measurement. The end play was re-measured, yielding 0.033 inch, thereby negating the required replacement. From that point until the accident, the average wear rate was approximately 0.010 inch per 1,000 flight hours, or ten times the nominal wear rate of 0.001 inch per 1,000 hours. The point is that diligent recording of the wear can yield important insight into the wear rate.
Source: http://www.ntsb.gov/events/2000/Aka261/docket/239227.pdf, p. 14, as modified by ASW
International Standing of Airworthiness Directives
European Aviation Safety Agency, Oct. 14, 2003, decision of the Executive Director (extracts):
“It is common practice for imported products, parts and appliances to rely on the state of design to first detect whether unsafe conditions require the issuing of an airworthiness directive.
“Any airworthiness directive issued by a state of design for an aircraft imported from a third country, or for an engine, propeller, part or appliance imported from a third country and installed on an aircraft registered in an EU [European Union] Member state, shall apply unless the Agency has issued a different Decision before the date of entry into force of that airworthiness directive.”
Source: EASA, Decision No. 2/2003