Vintage: The landing of Aloha Airlines Flight 243 in Hawaii, US, 32 years ago
32 years ago, on 28 April 1988, Aloha Airlines Flight 243 lost part of its roof in a serious decompression incident. Aloha Airlines Flight 243 was a scheduled Aloha Airlines flight between Hilo and Honolulu in Hawaii. On 28 April 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 aircraft. 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.
Aircraft and crew
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. 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.
Flight 243 departed from Hilo International Airport at 13h25 HST on 28 April 1988, with six crew members and 89 passengers on board, bound for Honolulu. 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.
After a routine takeoff and ascent, the aircraft had reached its normal flight altitude of 24 000 feet (7 300m), when at around 13h48, about 23 nautical miles (43km) south-southeast of Kahului on the island of Maui, a small section on the left side of the roof ruptured with a ‘whooshing’ sound. 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.” 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 (5,6m).
There was one fatality: 58-year-old flight attendant Clarabelle ‘CB’ Lansing, who was swept out of the airplane while standing near the fifth row seats; her body was never found. Lansing was a veteran flight attendant of 37 years at the time of the incident. Eight other people suffered serious injuries. All of the passengers had been seated and wearing their seat belts during the depressurisation.
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.
Extract from NTSB report:
No unusual occurrences were noted by either crewmember during the departure and climbout. As the airplane levelled at
24 000 feet, both pilots heard a loud “clap” or “whooshing” sound followed by a wind noise behind them. The first officer's head was jerked backward and she stated that debris, including pieces of grey insulation, was floating in the cockpit. The captain observed that the cockpit entry door was missing and that “there was blue sky where the first-class ceiling had been.” The captain immediately took over the controls of the airplane. He described the airplane attitude as rolling slightly left and right and that the flight controls felt “loose.”
Because of the decompression, both pilots and the air traffic controller in the observer seat donned their oxygen masks.
The captain began an emergency descent. He stated that he extended the speed brakes and descended at an indicated airspeed (IAS) of 280 to 290 knots. Because of ambient noise, the pilots initially used hand signals to communicate. The first officer stated that she observed a rate of descent of 4 100 feet per minute at some point during the emergency descent. The captain also stated that he actuated the passenger oxygen switch. The passenger oxygen manual tee handle was not actuated.
When the decompression occurred, all the passengers were seated and the seat belt sign was illuminated. The No 1 flight attendant reportedly was standing at seat row 5. According to passenger observations, the flight attendant was immediately swept out of the cabin through a hole in the left side of the fuselage. The No 2 flight attendant, standing by row 15/16, was thrown to the floor and sustained minor bruises. She was subsequently able to crawl up and down the aisle to render assistance and calm the passengers. The No 3 flight attendant, standing at row 2, was struck in the head by debris and thrown to the floor. She suffered serious injuries including a concussion and severe head lacerations.
The first officer said she tuned the transponder to emergency code 7700 and attempted to notify Honolulu Air Route Traffic Control Centre (ARTCC) that the flight was diverting to Maui. Because of the cockpit noise level, she could not hear any radio transmissions and she was not sure if the Honolulu ARTCC heard the communication.
Although Honolulu ARTCC did not receive the first officer's initial communication, the controller working flight 243 observed an emergency code 7700 transponder return about 23 nautical miles (nmi) south-southeast of the Kahalui Airport, Maui. Starting at 13h48:15, the controller attempted to communicate with the flight several times without success.
When the airplane descended through 14 000 feet, the first officer switched the radio to the Maui Tower frequency. At 13h48:35, she informed the tower of the rapid decompression, declared an emergency and stated the need for emergency equipment. Maui Tower acknowledged and began emergency notifications based on the first officer's report of decompression.
At the local controller's direction, the specialist working the Maui Tower clearance delivery position notified the airport's rescue and fire fighting personnel, via the direct hot line, that a B-737 had declared an emergency, was inbound and that the nature of the emergency was a decompression. Rescue vehicles took up alert positions along the left side of the runway.
At the Maui Airport, ambulance service was available from the nearby community when notified by control tower personnel through the local 9-1-1 telephone number. Tower personnel did not consider it necessary at that time to call for an ambulance based on their understanding of the nature of the emergency.
At 13h49:00, emergency coordination began between Honolulu Centre and Maui Approach Control. Honolulu advised Maui Approach Control that they had received an emergency code 7700 transponder return that could be an Aloha 737 and stated, “You might be prepared in case he heads your way.” Maui Approach Control then advised Honolulu Centre that flight 243 was diverting to land at Maui.
The local controller instructed flight 243 to change to the Maui Sector transponder code to identify the flight and indicate to surrounding air traffic control (ATC) facilities that the flight was being handled by the Maui ATC facility. The first officer changed the transponder as requested.
The flight was operating beyond the local controller's area of radar authority of about 13nmi. At 13h50:58, the local controller requested the flight to switch to 119,5MHz. (approach frequency) so that the approach controller could monitor the flight. Although the request was acknowledged, the flight was not heard on 119,5MHz. Flight 243 continued to transmit on the local controller frequency.
At 13h53:44, the first officer informed the local controller, “We're going to need assistance. We cannot communicate with the flight attendants. We'll need assistance for the passengers when we land.” An ambulance request was not initiated as a result of this radio call. The first officer also provided the local controller with the flight's passenger count but she did not indicate the fuel load. The local controller did not repeat the request for the fuel load even after a query from the chief of the emergency response team.
The captain stated that he began slowing the airplane as the flight approached 10 000 feet mean sea level (msl). This manoeuvre is required as a routine operations practice to comply with ATC speed limitations. He retracted the speed brakes, removed his oxygen mask and began a gradual turn toward Maui's runway 02. At 210 knots IAS, the flight crew could communicate verbally. The captain gave the command to lower the flaps. Initially flaps 1 were selected, then flaps 5. When attempting to extend beyond flaps 5, the airplane became less controllable and the captain decided to return to flaps 5 for the landing.
Because the captain found the airplane becoming less controllable below 170 knots IAS, he elected to use 170 knots IAS for the approach and landing. Using the public address (PA) system and on-board interphone, the first officer attempted to communicate with the flight attendants; however, there was no response.
At the command of the captain, the first officer lowered the landing gear at the normal point in the approach pattern. The main gear indicated down and locked; however, the nose gear position indicator light did not illuminate. Manual nose gear extension was selected and still the green indicator light did not illuminate; however, the red landing gear unsafe indicator light was not illuminated. After another manual attempt, the handle was placed down to complete the manual gear extension procedure. The captain said no attempt was made to use the nose gear downlock viewer because the centre jumpseat was occupied and the captain believed it was urgent to land the airplane immediately.
At 13h55:05, the first officer advised the tower, “We won't have a nose gear,” and at 13h56:14, the crew advised the tower, “We'll need all the equipment you've got.” While advancing the power levers to manoeuvre for the approach, the captain sensed a yawing motion and determined that the No 1 (left) engine had failed. At 170 to 200 knots IAS, he placed the No 1 engine start switch to the ‘flight’ position in an attempt to start the engine; there was no response. A normal descent profile was established 4 miles out on the final approach. The captain said that the airplane was “shaking a little, rocking slightly and felt springy.”
Flight 243 landed on runway 02 at Maui's Kahului Airport at 13h58:45. The captain said that he was able to make a normal touchdown and landing rollout. He used the No 2 engine thrust reverser and brakes to stop the airplane. During the latter part of the rollout, the flaps were extended to 40° as required for an evacuation. An emergency evacuation was then accomplished on the runway.
After the accident, a passenger stated that as she was boarding the airplane through the jet bridge at Hilo, she observed a longitudinal fuselage crack. The crack was in the upper row of rivets along the S-10L lap joint, about halfway between the cabin door and the edge of the jet bridge hood. She made no mention of the observation to the airline ground personnel or flight crew.
The aircraft was damaged beyond repair and was dismantled on site. Additional damage to the airplane included damaged and dented horizontal stabilisers, both of which had been struck by flying debris. Some of the metal debris had also struck the aircraft's vertical stabiliser, 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.
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. In the construction of this aircraft, this doubler sheet was not used in addition to other details of the bonding of the parts. In the case of production line 292 and after, this doubler sheet gave an additional thickness of 0,91mm at the lap joint. In airplane line number 291 and before, cold bonding had been utilised, 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 0,9mm 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 pressurisation 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.
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.
The NTSB concluded in its final report on the accident:
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.
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 recognises 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.
Sources: NTSB, Wikipedia and Wings News