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SR 111 Investigation Report

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1.6.22  Aircraft Maintenance Records and Inspection General Maintenance Records Maintenance Inspections MD-11 Service Information MD-11 Service Difficulty Reports MD-11 Maintenance Management

Back to the top  General (STI1-40)

The Maintenance System Approval Statement contained in Swissair's Air Operator Certificate (AOC) 1017 stated that Swissair was approved under Joint Aviation Requirements (JAR)-OPS 1, Subpart M, to manage the maintenance of its MD-11 aircraft. At the time of the occurrence, Swissair had contracted all aircraft maintenance to SR Technics, and Swissair had no in-house maintenance capability. As a JAR/FAR 145–approved repair station, SR Technics was contracted to perform all aircraft maintenance defect rectification, maintenance checks beyond the pre-flight, maintenance engineering activities, maintenance planning, and spare parts handling in support of Swissair's operations.

Back to the top  Maintenance Records

During the investigation, a review was conducted of Swissair/SR Technics' maintenance program, record-keeping procedures, and the occurrence aircraft's maintenance records. A small number of discrepancies were discovered regarding engineering orders (EO) and logbook entries. The discrepancies were considered minor, and the overall method of record-keeping was considered to be sound. The maintenance records kept for HB-IWF indicate that it was maintained in a manner commensurate with industry practices.

The review of the aircraft's maintenance records, which included the technical logbook entries from 10 September 1997 until 2 September 1998, the last three "A checks," and the IFEN System Maintenance Activity Review, did not identify any events that were considered relevant to the investigation.

Back to the top  Maintenance Inspections (STI1-41)

In addition to the maintenance checks carried out before every departure, Swissair MD-11s underwent a series of scheduled maintenance activities. These were accomplished at various flight hours (FH) as follows: "A check" every 700 FH; "C check" every 6 000 FH; and first "D check" at 30 000 FH or 72 months, whichever occurred first. The last scheduled maintenance activity carried out on the occurrence aircraft was an "A check" completed on 10 August 1998.

A review of HB-IWF's maintenance history verified that all requirements of the approved maintenance program were completed either on time, or within the tolerance granted to Swissair by the Swiss Federal Office for Civil Aviation (FOCA).

Back to the top  MD-11 Service Information  Service Bulletins (STI1-42)

Aircraft manufacturers and product vendors issue to users of their products, documents that are designed to improve the level of flight safety, to provide specific advice or instructions, or both. These documents include, but are not limited to, Service Bulletins (SB), Alert Service Bulletins (ASB), Service Letters, and All Operator Letters (AOL). The type of document issued depends upon the issuer's assessment of the urgency or severity of the information being presented; ASBs have the highest priority. Compliance with these documents is at the owner's or operator's discretion, as compliance is not mandatory unless an associated Airworthiness Directive (AD) is promulgated by the applicable regulatory authority.

At the time of the occurrence, there were 822 MD-11 SBs applicable by fuselage number to HB-IWF of which 51 were ASBs. Of the 51 ASBs, 47 were complied with, 2 were related to AD 94-10-03 for which an exemption was granted (see Section, 1 was underway, and 1 was specific to a water heater installation that was not installed in the Swissair fleet of MD-11s. The SR Technics engineering department reviewed each SB. If it determined that the SB warranted incorporation, they produced an EO. The determination to accept or reject an applicable SB was made by the cognizant engineer, and reviewed and approved by the cognizant engineer's manager.

A review of the aircraft manufacturer's MD-11 SBs issued up to the time of the accident identified 16 that were considered of interest to the investigation. Included in these were SBs related to events that could cause chafing, arcing, sparking, or smoke in the cabin or cockpit.   Airworthiness Directives (STI1-43)

An AD, typically based on either a manufacturer's or vendor's SB, is issued when an unsafe condition exists and that condition is likely to exist or develop in other products of the same type design. An AD is a regulatory directive mandating an inspection, repair, modification, or procedure issued either by the state of manufacture or by the CAA of the country in which the aircraft is registered.

The FOCA adopts and reissues each AD published by a state of manufacture pertaining to aircraft registered in Switzerland or with products that might be installed on Swiss-registered aircraft. Within SR Technics, the FOCA AD will only be distributed if it is not covered by an AD issued by the state of manufacture, or if there are deviations in the content. Swissair complied with all ADs issued by the state of manufacture, even if they were not legally binding for Swiss-registered aircraft under Swiss legislation.

At the time of the occurrence, 57 MD-11 ADs were issued by the FAA that were applicable to the occurrence aircraft. The SR Technics "Status List of Engineering Orders" verified that all applicable ADs had been accomplished, with the exception of AD 94-10-03, for which an exemption has been granted to Swissair by the FOCA. AD 94-10-03 addressed a potential software anomaly involving navigation equipment input to the FMC/FCC, and was therefore not deemed to be relevant to the circumstances of this occurrence. A review of the MD-11 ADs issued by the FAA up to the time of the accident identified the following two ADs that were potentially related to either the area of the fire damage in SR 111 (AD 93-04-01) or other smoke events in the cockpit (AD 97-10-12).

The subject of AD 93-04-01 was to "prevent display units from going blank, which could lead to momentary loss of flight critical display information." This AD took effect on 2 April 1993 and referred to ASB MD-11 A24-51, which took effect on 11 September 1992. SR Technics accomplished the AD on 14 January 1993 when the ASB was completed.

The subject of AD 97-10-12 was to "detect and correct chafing of the wire bundles adjacent to the avionics disconnect panel bracket assembly and consequent in-flight arcing behind the avionics CB panel, which could result in a fire in the wire bundles and smoke in the cockpit." This AD took effect on 16 June 1997 and referred to SB MD11-24-111, which took effect on 3 December 1996. SR Technics had accomplished this AD on HB-IWF on 6 March 1997.

Back to the top  MD-11 Service Difficulty Reports (STI1-44)

A search of the FAA's Service Difficulty Report (SDR) database for MD-11/11F entries, submitted until September 1998, revealed a total of 970 SDRs.[46] At that time, the MD-11/11F SDRs were reviewed using the keywords fire, smoke, and smell. Additionally, the same data was searched using the Air Transport Association (ATA) codes for communications (2300) system, power distribution (2400), and fire protection (2600) systems. This review revealed some general statistical information referred to in Section 1.18.10, but did not identify specific discrepancies relevant to the circumstances of this investigation. Detailed and specific information regarding wiring discrepancies was not consistently available as it was not required to be captured within the SDR database. There was no dedicated Joint Aircraft Systems/Components Inspection Code (enhanced ATA codes) used to collect, compile, and monitor data regarding wiring discrepancies. However, during the course of this investigation, on the basis of wiring data issues highlighted by National Transportation Safety Board (NTSB) investigations such as Trans World Airlines 800[47] and by industry group deliberations, the FAA requested that the ATA introduce a new ATA reporting code subchapter (97) to facilitate more accurate tracking of specific wire-related problems and anomalies.

Back to the top  MD-11 Maintenance Management

As with any commercial aircraft, the maintenance management of the MD-11 involved various companies and regulatory agencies. Beyond Swissair's maintenance obligations, as outlined in their AOC, SR Technics, the FOCA, the FAA, and Boeing all had either direct or indirect maintenance management commitments in support of Swissair's MD-11 fleet (see Section 1.17).

[46]    The FAA's Service Difficulty Report (SDR) system is designed to collect, analyze, record, and disseminate data concerning defects and malfunctions that have resulted in, or are likely to result in, a safety hazard to an aircraft or its occupants. Information contained in SDRs is submitted by the aviation community and is, for the most part, unverified.

[47]    See the National Transportation Safety Board report DCA96MA070 concerning the 17 July 1996 accident involving a Trans World Airlines Boeing 747-131 near East Moriches, New York.

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Updated: 2003-03-27

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