Electrical & Fuel System Problems Dominate Douglas Aircraft Airworthiness Directives

Air Safety Week, June 19, 2000

Some 40 percent of the airworthiness directives issued by the Federal Aviation Administration (FAA) on Douglas-built aircraft represent orders to fix electrical and fuel system-related problems. In this respect, Douglas aircraft have the dubious distinction of leading the worldwide jet fleet for problems in these areas.

AD's calling for inspections, repairs, modifications, etc., to electrical and fuel systems in Douglas aircraft exceed that of Airbus and Boeing-built airplanes in both absolute numbers and as a percentage of the AD's issued by fleet type. This finding emerges from a compilation of AD's issued over a twoyear period spanning April 1, 1998 to June 9, 2000. The resulting snapshot, prepared by Aviation DataSource, Inc., of Denver, provides an overview of a number of safety issues. April 1, 1998 was picked as a starting point for the reason that shortly thereafter the FAA issued emergency AD's calling for immediate inspection for chafed wires in fuel tank conduits of B737 aircraft. That activity led to the temporary grounding May 14, 1998 (Mother's Day in the U.S.) of many high-time 737's. At the time, the FAA was fearful that arcing could cause another fuel tank explosion of the type that downed TWA Flight 800 in 1996. The hunt for potential ignition sources in fuel tanks continues, as evidenced by the recent AD requiring operators to inspect for chafed wiring in the fuel tank conduits of Boeing 767 jets -- a virtual carbon copy of the 737 inspections of two years ago (see ASW, June 5).

A substantial portion of the Douglas AD's have been issued in the past four months. They clearly result from the ongoing program to assure the flight safety of MD-11 aircraft (see ASW, May 29). Of the 39 AD's issued on electrical and fuel systems in the past two years, 20 have been issued this year.

AD's addressing engines were not included in this review. Some 43 percent of the AD's deal with Boeing aircraft, which represent about 60 percent of the worldwide fleet. The roughly 2,000 Airbus jets in airline service represent 16 percent of the worldwide fleet; AD's addressing Airbus aircraft represent 33 percent of the total. Douglas aircraft comprise about 22 percent of the worldwide fleet and 21 percent of the AD's address Douglas aircraft. Lockheed's L-1011 constitutes a trivial one percent of the worldwide fleet and the AD's mostly deal with the structure of this vintage jet.

The dominance of AD's dealing with structural issues is not surprising. This category constitutes the "meat and potatoes" of AD activity as a consequence of the FAA's aging aircraft supplementary structural inspection program. Many Boeing aircraft are aging. More Airbus aircraft are showing their years. The volume of structure related AD's is consistent with the demographics of fleet aging.

Electrical and fuel system AD's make up the second largest category. AD's in this area deal with wiring, electrical components such as the recent call to inspect MD-11 map lights, fuel boost pumps, etc. - basically, anything that could potentially lead to an in-flight fire or explosion.

Boeing has the highest number of AD's in the flight control category - which reflects FAA efforts in such things as the 737 rudder power control unit and recent across-the-board inspections of jackscrews in horizontal stabilizers. Of interest is the relatively low number of AD's issued for avionics problems. >> Aviation DataSource, tel. 303/429-9606, e-mail Airbase@airresearch.com <<

Two Years of Airworthiness Directives
(April 1, 1998 - June 9, 2000)
Aircraft by Manufacturer
Number of Airworthiness  Directives by Category

E                                                S    C   A   M   Total
Boeing
34                                               81   41  4   33  193
Douglas
39                                               30   8   4   15  96
Airbus
15                                               70   31  10  21  147
Lockheed (L-1011 only)
2                                                7    1   1   2   13
Total
90                                               188  81  19  71  449

Legend:
E:  Electrical and Fuel System Related
S:  Structural
C: Control related
A:  Avionics
M:  Miscellaneous
Source:  Aviation DataSource