|Title:||Multiple electrical failures, Boeing 737-209, April 26, 1994|
|Micro summary:||The failure of the battery transfer relay resulted in multiple system failures during approach for this Boeing 737-209.|
|Event Time:||1994-04-26 at 1942 HST|
|Publishing Agency:||National Transportation Safety Board (NTSB)|
|Site of event:||Honolulu, HI|
|Departure:||Kona International Airport, Kailua-Kona, Hawaii|
|Destination:||Honolulu International Airport, Honolulu, Hawaii|
|Airplane Type(s):||Boeing 737-209|
|Type of flight:||Revenue|
NTSB short summary:
The failure of the battery transfer relay resulting in multiple system failures.
On approach, the crew lowered the landing gear, but noticed none of the gear position lights were illuminated. Prior to landing, the captain found both the public address and interphone to be inoperative. A visual approach was performed with a normal touchdown. During rollout, the crew discovered that the thrust reversers would not deploy. After turning off the runway, the flight attendants began to smell smoke. The captain stopped on the taxiway and initiated an emergency evacuation. One passenger received a minor sprain while using the emergency slide. An inspection revealed that a multiple system loss had occurred due to the 28-volt DC battery bus going off-line. The condition was duplicated during troubleshooting and the failed part was identified as a battery transfer relay (R2). The source of the on board smoke was not identified.
NTSB factual narrative text:
On April 26, 1994, at 1942 Hawaii standard time, one passenger sustained minor injuries during a slide evacuation of Aloha Airlines flight 289, at Honolulu, Hawaii. The aircraft, a Boeing 737-209, N804AL, experienced multiple system failures during the landing approach and the evacuation was prompted by smoke entering the cockpit and cabin. The remaining 53 passengers and five crew members were not injured. The aircraft was owned and operated by Aloha Airlines, Inc., and was on a scheduled domestic passenger flight under 14 CFR Part 121 of Federal Aviation Regulations. Visual meteorological conditions prevailed at the time and an IFR flight plan had been filed for the operation. The flight originated from Kona, Hawaii, at 1905 on the day of the incident.
According to the flight crew, during a visual approach into Honolulu International airport, the crew lowered the landing gear approximately 7 minutes from runway 4R. The gear extension appeared to be normal, but neither the red nor green position lights illuminated. System evaluation procedures revealed that the press-to-test function of the gear lights still operated; however, the master caution system was found to be inoperative.
The manual gear extension system was employed with no noticeable change or indication. The first officer went back to the cabin to check the main gear visually, but because he was not familiar with the sight location in this configuration, could not locate the view port on the cabin floor. The captain then elected to do a flyby on runway 4R at 1,000 feet above ground level (agl). The tower was unable to confirm that the gear was down. The crew then attempted another flyby on runway 8L at 800 feet agl, and both the tower personnel and the crew of another aircraft on the ground were able to confirm that the gear was down. The captain then attempted a public address call to the passengers and an interphone call to a flight attendant, but both systems were also found to be inoperative.
The captain did not declare an emergency, but requested that airport emergency equipment be prepositioned prior to landing. A visual approach was performed with a normal touchdown. During rollout, the crew discovered that the thrust reversers would not deploy. The aircraft was stopped using brakes and spoilers without further difficulty.
After turning off runway 8L onto taxiway alpha en route to the gate, the flight attendants noticed what was described as a "burning odor." One attendant opened the cockpit door and informed the captain of the smell. The captain reported that he had also noticed the odor. As the flight attendant opened the door to the cockpit, the smoke alarm went off in the forward lavatory. The flight attendant opened the door to the lavatory, but found no smoke visible inside. As the same attendant looked toward the rear of the aircraft, he noticed there was hazy smoke accumulating in the mid-to-aft portion of the passenger cabin. During this time, the attendant reported that all the lights had gone out in the cabin.
The captain stopped on the taxiway and instructed the crew to initiate an emergency evacuation. The evacuation was conducted with the assistance of the captain and first officer, using the emergency slides located at the forward service and entry doors. One attendant reported that after the doors were opened the smoke dissipated. Another attendant reported that the smoke alarm in the aft lavatory had also sounded during this time. The evacuation proceeded normally with the exception of one passenger who received a minor sprain while using the emergency slide. That passenger was treated at the scene and released. There were no injuries as a result of the events prior to the evacuation.
The crew also reported that while inbound to Honolulu the autopilot had disengaged and could not be reengaged. There was a computer flag reported on the captain's ADI. The circuit breakers were recycled without effect.
Investigation after landing revealed that the multiple system loss was due to the 28-volt DC battery bus going off-line. The condition was duplicated during troubleshooting and the failed part was identified as a battery transfer relay (R2). The source of the on board smoke was not identified.
All of the inoperative systems were identified as being powered by the battery bus. The aircraft operations manual does not specify a troubleshooting procedure for identifying a bus failure or multiple system electrical failure. There are no cockpit indications that directly identify a bus failure or multiple system failure. The Boeing representative reported that when multiple systems are lost, the loss of a bus should be a reasonable conclusion; however, none of the current checklists relate to this possible condition. He also stated that there is no procedure that would enable the flight crew to restore power to the effected systems once bus failure has been experienced.
A review of Federal Aviation Administration (FAA) safety data reports for the Boeing 737 aircraft failed to reveal any prior instances of relay or bus failures. Boeing reported two prior incidents, in 1971 and 1988, in which the battery bus lost power due to the failure of the R-1 battery relay. The failures were attributed to high resistance in the relay contact. The source of the resistance was identified as contact surface contamination caused by potassium bicarbonate residue.
The contamination occurred during the manufacturer's cleaning process. The surface contamination resulted in a voltage drop which then allowed the bus to go off-line. Boeing reported that the relay part manufacturer implemented manufacturing and process improvements to prevent cleaning material from contaminating the contact surface. There have been no reported discrepancies with R-1 relays manufactured after April 26, 1988.
|Learning Keywords:||Operations - Cabin or Cockpit Smoke|
|Operations - Evacuation|
|Systems - Electrical|
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