|Title:||Electrical failure, Boeing 767, June 19, 1996|
|Micro summary:||Dual generator failure results in a trip back to the gate on this Boeing 767.|
|Event Time:||1996-06-19 at 2322 MDT|
|Publishing Agency:||National Transportation Safety Board (NTSB)|
|Diversion Airport:||Salt Lake City International Airport, Salt Lake City, Utah, USA|
|Site of event:||Salt Lake City, UT|
|Departure:||Salt Lake City International Airport, Salt Lake City, Utah, USA|
|Destination:||Portland International Airport, Portland, Oregon, USA|
|Airplane Type(s):||Boeing 767-332|
|Operator(s):||Delta Air Lines|
|Type of flight:||Revenue|
|Diverted to:||Salt Lake City International Airport, Salt Lake City, Utah, USA|
NTSB short summary:
failure of maintenance personnel to properly disconnect (disengage) the right integrated drive generator (IDG) in compliance with the MEL dispatch procedure, which allowed the right IDG to overheat. Factors relating to the incident were: low oil pressure in the right IDG, and insufficiently defined company developed dispatch procedure.
During taxi for departure a 'R GEN OFF' and 'R GEN DRIVE' EICAS message illuminated indicating a malfunction of the right integrated drive generator (IDG), and the crew returned the Boeing 767 to the gate. Maintenance was notified, and a mechanic was dispatched to the aircraft. The mechanic reported that he 'assumed (the) crew had disconnected (the) IDG.' The captain reported that he was advised by the mechanic that 'the IDG is disconnected.' The aircraft was prepared and released according to its MEL for the flight using the left IDG and APU generator. During climbout a 'R STARTER CUTOUT' EICAS message illuminated followed by a fire warning on the right engine. Both fire bottles were exhausted, the fire warning extinguished, and the aircraft was returned to Salt Lake City, for emergency landing on runway 16L. Postincident examination of the engine revealed the fire-damaged remains of the right IDG and its magnesium housing. A download of digital data from the aircraft revealed that the original EICAS and IDG annunciations were related to low oil pressure within the IDG. An FAA inspector, who examined the aircraft immediately following the event, found the right IDG disconnect switch still safety wired (the IDG cannot be disconnected without breaking the wire and depressing the switch). The MEL dispatch procedure developed by the carrier did not address the need to run the associated engine at or above idle in order to successfully disconnect the IDG.
NTSB factual narrative text:
HISTORY OF FLIGHT
On June 19, 1996, at 2322 hours mountain daylight time, a Boeing 767-332, N136DL, being operated by Delta Airlines as flight 229, sustained minor damage when the number two (right) engine integrated drive generator (IDG) caught fire during a climb, approximately 80 nautical miles northwest of Salt Lake City, Utah. The Captain, First Officer, six cabin crew, and 178 passengers were uninjured. Visual meteorological conditions prevailed and an IFR flight plan was in effect. The flight, which was a regularly scheduled passenger flight operated under 14CFR121, departed Salt Lake City International airport at 2308 destined for Portland, Oregon.
During taxi for takeoff the crew observed both the "R GEN OFF" and "R GEN DRIVE" EICAS (engine indication and crew alerting system) messages and returned to the gate for corrective action. The captain reported that he "notified maintenance control and informed them that the aircraft was returning to the gate and informed them of the EICAS messages" and that the "after landing checklist was completed as well as the "generator off" abnormal procedure" (refer to ATTACHMENT I). He further reported that he "was turning the aircraft into the gate area, therefore further checklist procedures were discontinued pending examination of the aircraft by maintenance personnel." The aircraft's engines were then shut down.
According to the Captain, a mechanic was briefed on the problem and departed the flight deck with the aircraft log and minimum equipment list (MEL). Shortly thereafter, the mechanic returned with the aircraft log showing the discrepancy as having been signed off. The captain reported that he discussed the maintenance actions taken and was told by the mechanic that "the IDG is disconnected." The crew anticipated observing the generator drive light and right generator off light for the duration of the flight to Portland, and would be using the auxiliary power unit (APU) generator as a replacement for the right generator.
The mechanic reported that upon entering the cockpit he "found the right generator field light ON with (the) associated IDG drive light illuminated." He further reported that he "found the right generator drive disconnect switch released (and) assumed (the) crew had disconnected (the) IDG." The aircraft was subsequently dispatched in accordance with the MEL (refer to attached statement and ATTACHMENT II).
After an uneventful taxi, takeoff and departure, and while crossing flight level (FL) 250, the crew observed a "R STARTER CUTOUT" EICAS message and the overhead right starter valve light illuminated intermittently. The "Starter Cutout" procedure was accomplished following which a flight attendant reported that a passenger in the aft cabin, right side, had observed sparks coming from the right engine. This was confirmed by the First Officer's visual inspection.
The First Officer then returned to the flight deck and the crew initiated a return to Salt Lake City during which the right engine fire warning light illuminated. The right engine was shut down and both fuselage mounted fire bottles were exhausted into the right engine with the fire warning light ceasing shortly after the second bottle was fired. An uneventful single engine emergency landing was accomplished at 2343 on runway 16L at Salt Lake City, and the aircraft rolled to a stop in the vicinity of the taxiway H-3 exit (refer to DIAGRAM I). The Captain established radio communications with the aircraft rescue and fire fighting (ARFF) team. The left engine was shut down shortly after landing with the aircraft remaining on APU power. According to ARFF records maintained by Salt Lake City airport, the fire was contained approximately 7 minutes after the landing. The left engine was subsequently restarted and the aircraft was taxied to gate D-3 under ARFF escort after which the passengers were deplaned via the jetramp.
POST INCIDENT EXAMINATION AND INFORMATION
Onsite examination of the right engine by Federal Aviation Administration (FAA) inspectors from the Salt Lake City Flight Standards District Office revealed that the IDG had separated from the accessory section of the right engine. The remnants of the IDG, including what remained of its magnesium housing were removed. There was evidence of fire damage within the accessory section of the engine concentrated in the vicinity of the IDG and hydro-mechanical fuel control unit. A hole was observed burned through the starter gearcase adjacent to the IDG and the start valve actuator was burned away (refer to DIAGRAM II). No significant damage was noted within the engine core area and the titanium heat shield which separates the accessory section from the core had only a single hole burned through the aft vertical face aft of the IDG location. A single hole was observed burned through the engine core cowling and in alignment with the previously described heat shield hole.
Additionally, FAA inspectors confirmed that the shear wire on the cockpit stationed IDG disconnect switch was intact.
The fire detection element which activates the cockpit fire warning annunciator does not pass near the IDG but is situated near the hydro-mechanical fuel control unit. The aircraft's General Electric CF6-80A engines are equipped with a titanium heat shield which separates the accessory section from the engine core. Engines not equipped with this heat shield (Pratt & Whitney and Rolls Royce) are equipped with a second fire detection element within the accessory section.
There is only one procedure (exclusive of removal) for physically disconnecting an IDG from its associated engine. The procedure entails breaking the shear wire which holds the clear plastic guard over the disconnect switch. This allows the hinged plastic guard to be rotated away from the square, push-button disconnect switch. The switch can then be depressed (refer to DIAGRAM III). When the switch is depressed it initiates the physical disconnection of the IDG from the engine, thus preventing rotation of the IDG armature. This procedure may be accomplished by the flight crew during flight or ground taxi operations by executing the "GENERATOR DRIVE" abnormal checklist with the engines running (ATTACHMENT I), or by maintenance as part of the MEL dispatch procedure for an inoperative left or right IDG (refer to ATTACHMENT II, pages one and two). This latter procedure (ATTACHMENT II) was a procedure developed by Delta Airlines from the Boeing 767 Dispatch Deviations Guide. In order for an IDG to be properly disconnected during this maintenance procedure without damaging the IDG's "disconnect dog teeth," it is necessary to start and run the associated engine at or above idle power before carrying out the disconnect procedure (item "C" of ATTACHMENT II, page one).
TESTS AND RESEARCH
A readout of digital data downloaded from the aircraft revealed that original IDG light and EICAS messages observed by the flight crew on initial taxi were related to low oil pressure within the IDG, and that the fire warning light observed by the crew during climbout extinguished shortly after the second fire bottle was exhausted into the right engine.
|Learning Keywords:||Operations - Maintenance|
|Systems - Electrical|
|Systems - Engine Fire|
|Close match:||CSD overheat resulting in engine shutdown, Boeing 747-136, June 17, 1996|
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