A Matter of Millimeters: The story of Qantas flight 32

42 min readDec 9, 2023--Officials observe damage to the engine of a Qantas A380 after it made an emergency landing in Singapore. (Reuters)On the 4th of November 2010, a Qantas Airbus A380 was rocked by a catastrophic engine failure minutes after takeoff from Singapore, hurling fragments of a turbine disk through its wings and fuselage in multiple locations. The explosion damaged almost every major system on the airplane, from the flight controls and fuel tanks to hydraulics and pneumatics. Faced with a barrage of diverse failure warnings and an airplane of uncertain integrity, the flight crew worked together to make a series of critical decisions that would get their enormous airplane back on the ground. And in the end, despite one curveball after another — including landing gear problems, loss of braking power, and an engine that refused to shut down — they not only landed the plane, but did so without putting a scratch on any of the 469 passengers and crew.The cause of the incident would ultimately be traced deep inside the number two engine to a single oil pipe that had been manufactured with a wall that was slightly too thin. How this seemingly tiny defect came about, and how it nearly brought down the world’s largest passenger plane, represent a story equally as fascinating as that of the flight itself, tracing back years to encompass questionable drawing board decisions, hidden flaws in the machining logic, and faulty assumptions about engine behavior. Time and time again, the problem slipped through the gaps in the system, tumbling down the long slope toward disaster — only to be stopped at the last moment, not only by the pilots themselves, but by a number of explicit protections built into the design of the A380, each of which played a crucial role in containing the fallout from a failure that exceeded the manufacturer’s worst expectations. The story of Qantas flight 32, as told herein, is therefore not only the tale of a dramatic emergency, but a testament to the safety of aviation today — a story that should make every reader feel a little less fearful of flight.◊◊◊Press enter or click to view image in full sizeA brand new Airbus A380 takes to the skies. (Pascal Le Segretain)Introduced to service in 2007, the double decker, four-engine A380 is by far the largest passenger aircraft in the world, exceeding the vaunted Boeing 747 in almost every measurement. Awesome to behold and pleasant to fly, there’s not much to dislike about the A380 — unless you’re an airline, in which case most major carriers dismissed the behemoth as too large for their operating models. Indeed, analysts’ assessment today is that the A380 was built for a market that had shrunk considerably by the time it actually entered service, and as a result, production ended in 2021 with only 254 built, some of which have already been scrapped. For an extraordinarily expensive aircraft equipped with some of the most advanced technology of any airliner, the collective result of immense effort and imagination, such a fate is unfortunate, but the reasons behind it, and the future of the type, are topics for a different article.Despite the above, some airlines did find the A380 suitable for their operations, including Qantas, the flag carrier of Australia. Qantas ordered 12 A380s to be delivered in 2008, of which ten are still flying today. It was the very first of these, registered as VH-OQA and nicknamed Nancy-Bird Walton after the pioneering Australian aviator, that would come to be involved in the events of the 4th of November 2010.Press enter or click to view image in full sizeVH-OQA, the aircraft involved in the accident. (Andrei Dimofte)On that date, VH-OQA arrived in Singapore for a scheduled stopover on a marathon London-to-Sydney trip, where it took on fuel, passengers, and a new flight crew for the last leg to Australia. The plane was essentially full, with 440 of 450 passenger seats filled, plus a massive complement of 29 crewmembers, including no less than five pilots. Although the A380 is normally flown by only two pilots, Qantas had also rostered a second officer as a relief crewmember; a check airman was conducting a line check on the captain; and another check airman was training the first check airman, so the cockpit was certainly crowded.In command, and under examination, was 53-year-old Captain Richard Champion de Crespigny, a veteran airman with over 15,000 hours of experience and 32 years in aviation. The other crewmembers consisted of First Officer Matt Hicks, Second Officer Mark Johnson, Check Captain Harry Wubben, and Senior Check Captain David Evans. The five crewmembers had a combined 140 years in aviation and 71,000 hours of flying experience, an incredible total that is rarely equaled.At 9:56 a.m. local time, with Captain de Crespigny at the controls, Qantas flight 32 departed Singapore and proceeded southeast across the strait toward Indonesia, passing over the densely populated island of Batam. All parameters still appeared normal as the A380 climbed through 7,000 feet, four minutes after takeoff. There was no indication that a catastrophic failure was in fact just seconds away.◊◊◊Press enter or click to view image in full sizeA Rolls-Royce Trent 900 engine with a man for scale. (Wikimedia user Tangopaso)The Airbus A380 is powered by four massive Rolls-Royce RB211 Trent 900-series high-bypass turbofan engines, each producing up to 84,000 lbf of thrust. Designed specifically for the A380, the Trent 900 was produced at several locations in the United Kingdom and was sold in competition with the American-built GP7200 jointly developed by Pratt & Whitney and General Electric.Understanding what happened aboard Qantas flight 32 requires that I subject you to a description of the structure of certain very specific parts of the engine.Like all high-bypass jet engines, the Trent 900 consists of four main sections: the fan, the compressors, the combustion chamber, and the turbines. During normal operation, air is forced backward and pressurized by a series of increasingly powerful compressors before being fed into the combustion chamber, where it is mixed with fuel and ignited. The combustion creates mechanical energy that spins a series of turbines, which in turn power the compressors, as well as the fan at the front of the engine, which accelerates large quantities of so-called bypass air around the outside of the engine core to generate most of the thrust output.Press enter or click to view image in full sizeLocations of turbines and compressors on the Trent 900. (FAA)Most turbofan engines examined in my articles have a high pressure compressor and a low pressure compressor, which correspond to high- and low-pressure turbines. These turbines are connected to their respective compressor sections by concentric drive shafts. However, the Trent 900 differs from this layout slightly, because it also has an intermediate pressure compressor with a corresponding intermediate pressure turbine, in between the high and low pressure sections. It also differs in that the fan itself doubles as the low pressure compressor. (From now on, for brevity’s sake, the abbreviations LP, IP, and HP will be used for low pressure, intermediate pressure, and high pressure, respectively.)Press enter or click to view image in full sizeIn this cutaway diagram of the IP turbine area, I’ve drawn blue boxes around the components mentioned in the following paragraph. (ATSB)On the Trent 900, the HP and IP turbine sections at the rear of the engine each consist of a single-stage turbine disk. Blades around the circumference of each disk capture mechanical energy from hot combustion gases flowing through what is known as the “annulus gas path.” These gases spin the disk, which is attached by a drive arm to its associated drive shaft. The shaft then transfers the turbine’s rotational energy forward to the corresponding compressor at the front of the engine.Press enter or click to view image in full sizeThis clip from an FAA video helps visualize the cutaway of the HP/IP bearing assembly. Note the location of the bearing chamber, which is depicted full of oil, and the pipe leading into it. Watch the full video here: https://www.youtube.com/watch?v=sYxVin_FFxQIn order to support the turbine disks and shafts while still allowing them to rotate freely, the engine features a complex system of bearings. The HP and IP turbine sections have a common bearing assembly, called the HP/IP bearing hub, which encircles the drive shafts and holds them in place while allowing free rotation of the shafts within.To prevent wear on the bearings, the space inside the bearing hub, called the bearing chamber, is constantly filled with pressurized oil that keeps everything gliding smoothly. This oil is supplied primarily by an oil feed pipe that runs from the main engine oil supply, past the annulus gas path, and down into the HP/IP bearing hub, where it injects oil through a filter and into the bearing chamber.The structure of the bearing hub consists of an inner and outer hub section, such that an empty buffer space exists between the bearing chamber and the rest of the engine. The oil feed pipe runs through both sections in order to reach the bearing chamber. The last segment of this pipe, a few centimeters in length, is welded in place during manufacture of the bearing hub, and the main portion of the pipe is fitted to it later. This fixed final segment that passes through the buffer space between the inner and outer sections of the HP/IP bearing hub is called the “stub pipe.”For reasons that will be examined in detail later, this tiny oil feed stub pipe triggered an escalating sequence of events within the space of mere seconds as Qantas flight 32 climbed away from Singapore.Within the №2 engine, located in the inboard position on the left wing, a crack in the oil feed stub pipe caused it to begin leaking oil less than four minutes after takeoff. The leak was small, but the