Fuselage remains after the emergency landing
|Date||April 28, 1988|
|Summary||Explosive decompression caused by metal fatigue and maintenance error|
|Aircraft type||Boeing 737-297|
|Aircraft name||Queen Liliuokalani|
|Flight origin||Hilo Int'l Airport (ITO)|
|Destination||Honolulu Int'l Airport (Now Daniel K. Int'l Airport) (HNL)|
Aloha Airlines Flight 243 (IATA: AQ243, ICAO: AAH243) was a scheduled Aloha Airlines flight between Hilo and Honolulu in Hawaii. On April 28, 1988, a Boeing 737-297 serving the flight suffered extensive damage after an explosive decompression in flight, but was able to land safely at Kahului Airport on Maui. There was one fatality, flight attendant Clarabelle Lansing, who was ejected from the airplane. Another 65 passengers and crew were injured. Despite the substantial damage inflicted by the decompression, and the loss of one cabin crew member, the safe landing of the aircraft established the incident as a significant event in the history of aviation, with far-reaching effects on aviation safety policies and procedures.
The aircraft involved was the 152nd Boeing 737 airframe. It was built in 1969 and delivered to Aloha Airlines as a new aircraft. Its registration was N73711 and it was named Queen Liliuokalani after Lili'uokalani. While the airframe had accumulated 35,496 flight hours prior to the accident, those hours included over 89,680 flight cycles (takeoffs and landings), owing to its use on short flights. This amounted to more than twice the number of flight cycles it was designed for.
The captain of the flight was 44-year-old Robert (Bob) Schornstheimer, an experienced pilot with 8,500 flight hours, 6,700 of which were in Boeing 737s.:11 The first officer was 36-year-old Madeline "Mimi" Tompkins; who also had significant experience flying the 737, having logged 3,500 of her total 8,000 flight hours in that particular Boeing model.:11
Flight 243 departed from Hilo International Airport at 13:25 HST on April 28, 1988, with six crew members and 89 passengers on board, bound for Honolulu.:2 Nothing unusual was noted during the pre-departure inspection of the aircraft, which had already completed three round-trip flights from Honolulu to Hilo, Maui, and Kauai earlier that day, all uneventful. Meteorological conditions were checked but there were no advisories for weather phenomena reported along the air route, per AIRMETs or SIGMETs.:2
After a routine takeoff and ascent, the aircraft had reached its normal flight altitude of 24,000 feet (7,300 m), when at around 13:48, about 23 nautical miles (43 km; 26 mi) south-southeast of Kahului on the island of Maui, a small section on the left side of the roof ruptured with a "whooshing" sound.:2 The captain felt the aircraft roll to the left and right, and the controls went loose; the first officer noticed pieces of grey insulation floating above the cabin. The cockpit door had broken away and the captain could see "blue sky where the first-class ceiling had been.":2 The resulting explosive decompression had torn off a large section of the roof, consisting of the entire top half of the aircraft skin extending from just behind the cockpit to the fore-wing area, a length of about 18.5 feet (5.6 m).
There was one fatality: 58-year-old flight attendant Clarabelle "C.B." Lansing, who was swept out of the airplane while standing near the fifth row seats; her body was never found.:5 Lansing was a veteran flight attendant of 37 years at the time of the incident. Eight other people suffered serious injuries.:5 All of the passengers had been seated and wearing their seat belts during the depressurization.
Co-pilot Tompkins was flying the aircraft when the incident occurred; Captain Schornstheimer took over and steered the aircraft toward the closest airport, on Maui island. Thirteen minutes later, the crew performed an emergency landing on Kahului Airport's Runway 2. Upon landing, the aircraft's emergency evacuation slides were deployed and passengers quickly evacuated from the aircraft. A total of 65 people were reported injured, eight of them with serious injuries. At the time, Maui had no plan in place for an emergency of this type. The injured were taken to the hospital in tour vans belonging to Akamai Tours (now defunct), driven by office personnel and mechanics, as the island only had two ambulances. Air traffic control radioed Akamai and requested as many of their 15-passenger vans as they could spare to go to the airport (three miles from their base) to transport the injured. Two of the Akamai drivers were former paramedics and established a triage on the runway. The aircraft was written off.
The aircraft was damaged beyond repair and was dismantled on site. Additional damage to the airplane included damaged and dented horizontal stabilizers, both of which had been struck by flying debris. Some of the metal debris had also struck the aircraft's vertical stabilizer, causing slight damage. The leading edges of both wings and both engine cowlings had also sustained damage.
The piece of the fuselage blown off the aircraft was never found. Investigation by the United States National Transportation Safety Board (NTSB) concluded that the accident was caused by metal fatigue exacerbated by crevice corrosion. The aircraft was 19 years old and operated in a coastal environment, with exposure to salt and humidity.
During an interview, passenger Gayle Yamamoto told investigators that she had noticed a crack in the fuselage upon boarding, but did not notify anyone.:5
For the aircraft production number 292 (B-737) and after (this aircraft was production line number 152), an additional outer layer of skin or doubler sheet at the lap joint of the fuselage was added.:16-17 In the construction of this aircraft, this doubler sheet was not used in addition to other details of the bonding of the parts.[clarification needed] In the case of production line 292 and after, this doubler sheet gave an additional thickness of 0.91 mm (0.036 in) at the lap joint. In airplane line number 291 and before, cold bonding had been utilized, with fasteners used to maintain surface contact in the joint, allowing bonding adhesive to transfer load within the joint. This cold bonded joint used an epoxy-impregnated woven scrim cloth to join the edges of 0.9 mm thick skin panels. These epoxy cloths were reactive at room temperature, so they were stored at dry ice temperatures until used in manufacture. The bond cured at room temperature after assembly. The cold bonding process reduced the overall weight and manufacturing cost. Fuselage hoop loads (circumferential loads within the skins due to pressurization of the cabin) were intended to be transferred through the bonded joint, rather than through the rivets, allowing the use of lighter, thinner fuselage skin panels with no degradation in fatigue life.:13-21
The additional outer layer construction improved the joint by:
The investigation determined that the quality of inspection and maintenance programs was deficient. As fuselage examinations were scheduled during the night, this made it more difficult to carry out an adequate inspection of the aircraft's outer skin.
Also, the fuselage failure initiated in the lap joint along S-10L; the failure mechanism was a result of multiple site fatigue cracking of the skin adjacent to rivet holes along the lap joint upper rivet row and tear strap disbond, which negated the fail-safe characteristics of the fuselage. Finally, the fatigue cracking initiated from the knife edge associated with the countersunk lap joint rivet holes; the knife edge concentrated stresses that were transferred through the rivets because of lap joint disbonding.:71
The NTSB concluded in its final report on the accident::73-74
The National Transportation Safety Board determines that the probable cause of this accident was the failure of the Aloha Airlines maintenance program to detect the presence of significant disbonding and fatigue damage which ultimately led to failure of the lap joint at S-10L and the separation of the fuselage upper lobe. Contributing to the accident were the failure of Aloha Airlines management to supervise properly its maintenance force; the failure of the FAA to require Airworthiness Directive 87-21-08 inspection of all the lap joints proposed by Boeing Alert Service Bulletin SB 737-53A1039; and the lack of a complete terminating action (neither generated by Boeing nor required by the FAA) after the discovery of early production difficulties in the B-737 cold bond lap joint which resulted in low bond durability, corrosion, and premature fatigue cracking.
One board member dissented, arguing that the fatigue cracking was clearly the probable cause, but that Aloha Airlines maintenance should not be singled out because failures by the FAA, Boeing, and Aloha Airlines Maintenance each were contributing factors to the disaster.:78
Pressure vessel engineer Matt Austin has proposed an additional hypothesis to explain the scale of the damage to Flight 243. This explanation postulates that initially the fuselage failed as intended and opened a ten-inch square vent. As the cabin air escaped at over 700 mph, flight attendant Lansing became wedged in the vent instead of being immediately thrown clear of the aircraft. The blockage would have immediately created a pressure spike in the escaping air, producing a fluid hammer (or "water hammer") effect, which tore the jet apart. The NTSB recognizes this hypothesis, but the board does not share the conclusion. Former NTSB investigator Brian Richardson, who led the NTSB study of Flight 243, believes the fluid hammer explanation deserves further study.