Dead-Stick Night Landing

Portuguese aviation authorities have issued their final accident report on Air Transat Flight 236, the Airbus A330-243 whose crew made a dead-stick night landing in the Azores after running out of fuel. The report is a sobering reminder of how quickly things can go wrong when individuals disregard or misunderstand the safeguards put in place to ensure safe operation of aircraft and complex systems. At the same time, it illustrates how good overall flying skills can salvage an otherwise disastrous situation — even if it was self-induced.

You probably recall the news accounts of the event, which happened on August 24, 2001. The twinjet widebody aircraft had departed Toronto, Canada's Lester B. Pearson International Airport en route to Lisbon Airport in Portugal. Both engines flamed out while the aircraft was still some 78 miles from Lajes Airport on Terceira Island in the Azores. The aircraft glided for 19 minutes before the crew landed on 10,866-foot-long Runway 33. The aircraft was moderately damaged, but all 293 passengers and 13 crewmembers aboard survived. During the emergency evacuation, 16 passengers and two crewmembers received minor injuries.

Breakdowns

How does something of this magnitude happen? As with most aviation accidents, multiple safeguards must break down before an accident becomes unavoidable. In this case the first breakdown occurred more than a week earlier. That's when Air Transat's maintenance department noted metal particles in the oil of the right engine. It was the second such discovery of metal particles in that engine's oil, and as a precaution the company decided to perform an engine change.

The airline did not have a spare on hand, so it requested one from engine manufacturer Rolls-Royce, which lent it an engine that had been in storage for a year. The engine change proceeded normally until the lead mechanic discovered that the engine hydraulic pump, taken from the original engine, didn't quite match up with the hydraulic line fittings on the new engine.

A service bulletin had been previously issued that modified the pump installation to provide more clearance between a hydraulic line and a nearby fuel line. All of Air Transat's engines had already been modified, but the stored loaner engine had not. The engine change team did not have a copy of the service bulletin to reference, but believed the change could be safely completed without it. The mechanics did so and released the aircraft to the line. Sometime during subsequent flights, vibration and flexing of the hydraulic line caused it to come in contact with the fuel line.

Dropping fuel

One week and 67.5 engine hours later, the fuel line finally cracked as Air Transat 236 flew through the night skies over the North Atlantic. It was 0438 Zulu (Coordinated Universal Time), and fuel began dumping overboard at a rate of about 1,000 pounds per hour. At this point the tanks contained a little more than 47,000 pounds.

Twenty minutes later, at 0458, Air Transat 236 crossed a position of 30 degrees west on the North Atlantic Track system, the "50-yard line," or halfway point, where air traffic control authority passes from Gander Oceanic Control to Shanwick Oceanic Control. In that short time the crack had widened, and the rate of fuel loss had increased to more than 9,000 pounds per hour. The crew made a standard position report and recorded various entries in the flight log. While making these entries the crew noted unusual indications in the number-two-engine oil system. Pressure was higher than usual, temperature was much lower, and the oil quantity had dropped noticeably from the last check. Fuel quantity as recorded in the log was as yet unremarkable, since it was only about 1 percent less than the crew expected to see when passing 30 degrees west.

The crew could not explain the strange oil system readings. Crewmembers contacted their company via high-frequency radio and conferred with the maintenance department, which promised to get back to them with an answer.

Unbeknown to the crew, there was a very good reason for the unusual readings. The fuel leak was letting much more fuel than usual flow through the engine's fuel/oil heat exchanger, which was upstream of the leak. The heat exchanger uses fuel to cool the engine oil. At the same time, it extracts heat from the oil to warm the fuel just before it enters the engine. This melts any ice crystals that might form in the cold soaked fuel at high altitudes, and which could clog the engine's fuel filters. The growing torrent of fuel through the heat exchanger was chilling the oil faster than the engine could heat it back up, causing the odd readings.

While the crew continued to troubleshoot the problem, the aircraft's Electronic Centralized Aircraft Monitoring (ECAM) system displayed the first of a series of fuel advisory messages to the crew. The messages detailed the automatic transfer of fuel from the aircraft's trim tank, located in the horizontal stabilizer, to the right wing tank. The system is designed to improve fuel efficiency by keeping the aircraft in an optimum center-of-gravity range. The computer had noted the dropping fuel quantity in the right-side tanks and was attempting to maintain balance. It continued to do so until all the trim tank fuel had transferred to the right side by 0530 Zulu. The crew, preoccupied with the oil issue, didn't note the series of fuel transfers as being unusual, even though the final transfer usually occurs much later in a flight.

Three minutes later, at 0533 Zulu, the pilots received an advisory message on the engine/warning display. This was triggered by the growing fuel imbalance, which now exceeded 3,000 pounds. The crack had enlarged further, and fuel from the right wing was now gushing overboard at more than 27,000 pounds an hour. In response to the imbalance and operating from memory, the captain opened the fuel crossfeed valve and turned off the right-side fuel pumps. Now both engines were burning fuel from the left-side wing tanks.

A fuel imbalance is considered an abnormal condition, and there is a quick reference handbook (QRH) procedure that Airbus crews are expected to reference before crossfeeding. Although the crossfeed procedure itself is simple enough and might easily be done from memory, the QRH begins with a caution note that warns, "Do not apply this procedure if fuel leak is suspected. Refer to Fuel Leak procedure." The note exists specifically to account for the rare possibility of an actual leak, as opposed to the more common kind of imbalance caused by unequal fuel burn or loading.

The procedure calls for the crew to ensure that the fuel crossfeed remains closed, and if a leak is believed to be in an engine, to shut it down. Keeping the crossfeed closed would have preserved the fuel remaining in the left-side wing tanks. Because the crew opened the crossfeed without reference to this checklist, it allowed the left-side fuel to feed the leak too.

Questions

Shortly after opening the crossfeed, the crew noted for the first time that fuel quantity was about 17,000 pounds less than expected. Neither pilot had ever experienced such a thing before. With this following so closely on the heels of the strange oil system readings, the pilots concluded it was probably an indication problem and not a real fuel loss. Perhaps a computer malfunction of some kind was to blame.

They were now hundreds of miles from the nearest land and 51 minutes away from complete fuel exhaustion. By 0545, just 12 minutes after noting the fuel imbalance, they calculated that there was insufficient fuel to reach Lisbon if in fact the fuel quantity was to be believed. As a precaution they decided to divert to Lajes. But according to their own later testimony, they still didn't believe they were losing fuel.

At 0552 another ECAM advisory message indicated a temporary fuel pressure loss on the right side, which corrected itself. Over the next 15 minutes they were extremely busy, conferring with ATC, their company, and the flight attendants. They asked a flight attendant to look for signs of a fuel leak, but in the dark the flight attendant saw nothing unusual through the cabin windows. While not conclusive, this report seemed to confirm their suspicions that there was no real fuel leak.

At 0554 they reversed the direction of the crossfeed, feeding from the right tank to both engines.

At 0558 ECAM presented another advisory message, triggered by fuel in the right wing having reached a minimum level.

At 0602 they switched the crossfeed again, returning to feeding both engines from the left tank.

At 0608 ECAM gave another advisory message, this time indicating that fuel in both wings had reached a minimum level. The pilots discussed the latest message, and noted for the first time that they no longer had enough fuel to reach Lajes, if the fuel quantity was accurate.

At 0613 the right engine flamed out because of fuel exhaustion, followed by the left engine 13 minutes later. The aircraft and crew were now still 78 miles from the airport, descending through Flight Level 345.

A resourceful crew

With no electrical generators, the aircraft was on battery power. The high-tech glass cockpit was reduced to just a handful of backup instruments. Normal hydraulic power was gone too, but a wind-driven Ram Air Turbine that dropped from the belly supplied enough hydraulic power to allow the captain to hand-fly toward the island.

Fortunately the crew picked up the flashing runway lights while still many miles away. The airplane arrived eight miles from the runway still at 13,000 feet, too high to land straight ahead. The captain flew a 360-degree turn to lose altitude, crossed the fence at about 200 knots, and hit hard 1,030 feet down the runway. After a single hard bounce, the aircraft settled on the runway and came to a stop.

The final report reaches 12 conclusions as to the cause of the accident and contributing factors. The first seven implicate Air Transat maintenance procedures that allowed the engine change to take place using faulty procedures. The remaining five involve the actions of the flight crew. Chief among these was the crewmembers' decision to conduct the fuel crossfeed from memory, causing them to miss the Fuel Leak checklist procedure. Had they followed this procedure, they would have preserved enough fuel in the left wing tanks to reach Lajes with only the right engine shut down.

While squarely blaming the crew-members for not preventing the accident in the first place, the report does credit them for their professional handling of the engine failures and subsequent dead-stick approach and landing, averting a potential disaster.

Vincent Czaplyski holds ATP and CFI certificates. He flies as a Boeing 737 captain for a major U.S. airline.