What ails aircraft engines these days and are more better?

Do more engines make a plane safer? The short answer is, "No". Aircraft have gone from eight engines to six, four and then two (considered adequate for passenger jet flight today). Pictured here is the impressive six-engine Antonov An225 that is alas no more. It perished in a 2022 airport bombing raid.

WHY are aircraft engines failing with such seeming regularity? It is a question air passengers are rightly asking these days as inflight engine shutdowns and aircraft groundings due to mechanical failures grab the headlines.

Cathay Pacific brought this issue to the fore anew when it grounded its Airbus A350 fleet following a problem on a Zurich-bound A350-1000 from Hong Kong. CX383 lost one engine shortly after take-off on 2 September 2024 and landed safely back in Hong Kong after dumping fuel. The grounding was temporary and focused on a fuel nozzle failure in the Rolls-Royce Trent XWB-97 engine that affected 15 aircraft. No one was injured. But an engine had failed. Again.

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This was not an isolated incident. At time of writing, airlines and aircraft types involving engine failures in 2024 already included United (B787 Dreamliner), Southwest (B737), American Airlines (A319), Delta (A330 and B767-400ER), and Alaska Airlines (737-700).

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Aircraft engines are built to last while generating thrust of up to 90,000lbf (pounds-force) as on a giant Rolls-Royce Trent that has over 30,000 individual parts.

Widebody aircraft are built to last an average 30,000-40,000 flight cycles (with a first engine overhaul at 20,000 cycles). A flight cycle is the sequence from take-off to landing. On robust narrowbody aircraft the stresses are higher with frequent daily cycles due to the short turnaround nature of the flights. Narrowbody planes can safely fly up to 50,000 cycles but their first engine overhaul will be at around 12,000 cycles.

{Widebody aircraft are built to last an average 30,000-40,000 take-off and landing flight cycles with a first engine overhaul at around 20,000 cycles...

A single plane may typically run through up to four engines during its lifespan. Engines last for up to three overhauls with the frequency (and cost) increasing after the first check as parts get replaced.

Widebody aircraft like the Jumbo B747 — some flying for over 30 years, the oldest thought to be in Iran — are still in service, and Air Force One that transports the US president is perhaps this model’s most recognisable face. Interestingly, Boeing was commissioned in 2018 to build two new 747s (to be flown as Air Force One) both due for delivery late 2024. With Boeing’s current problems, this delivery has been delayed to perhaps 2028.

Another sturdy Boeing jet pioneer that launched in 1957 — the screechy B707 — continues to fly as a private jet as well as with various air forces and cargo companies. Clearly, given optimal maintenance, aircraft longevity is not the issue.

The Federal Aviation Administration (FAA) calculates modern jet engine failures at one in 375,000 flying hours (or about once every 44 years of flying). This seems statistically reassuring. So, with the barrage of checks and scrutiny, why are engines failing?

The answer to this is somewhat mundane. Collectively, the biggest culprit is human error, whether due to sloppy maintenance, incorrect fuelling procedures (a common culprit), or erroneous piloting decisions. Other reasons include bird strikes, foreign debris getting into the engines, software glitches, and challenging weather.

On 24 August 2001, an Air Transat A330 Flight 236 from Toronto to Lisbon ran into trouble over the Atlantic following a fuel leak. Misreading the gauges the pilots cross-fed fuel to the “leaking” engine instead of shutting it down and nursing the remaining fuel for the one operable engine. The result was the loss of both engines. An experienced glider pilot, captain Robert Piche diverted to the Azores, without power, ‘gliding’ just over 120km to execute a perfect hard landing that won plaudits and praise even as disciplinary proceedings kicked in.

This was not the first time that a fuel miscalculation caused a near catastrophic problem. On 23 July 1983 Air Canada B767 Flight 143 flying Montreal to Edmonton lost both engines 41,000ft over Ontario. Captain Robert ‘Bob’ Pearson and first officer Maurice Quintal, did their calculations and guided the plane in a glide to Gimli where they landed on an abandoned racetrack with no loss of life.

This remarkable incident earned the aircraft the name, “The Gimli Glider”. It returned to service and flew until 2008. The fuel issue? Canada was in the process of switching from imperial to metric and the fuelling staff inadvertently miscalculated the required weight. With the cockpit crew on the B767 reduced from three to two (dropping the flight engineer who would have been responsible for the fuel log), the error slipped through.

Airline passengers should take heart. Engines are sturdy enough and planes can fly on just one. The eight-engine Hughes H4 Hercules “Spruce Goose” may have been the largest plane ever conceived. It made just one flight on 2 November 1947 but missed the war effort, for which it was intended. The four-engine A340 became too expensive to operate in a twin-engine world that speedily overtook it after Extended-range Twin-engine Operations Performance Standards (ETOPS) regulations were relaxed.

The huge six-engine Antonov An-225 ‘Mriya’ may have been the safest plane ever with its huge redundancy array. We’ll never find out as the sole Ukrainian-built cargo aircraft was destroyed in a Russian air strike in 2022 on Kyiv’s Antonov Airport.

While the National Aeronautics and Space Administration attributes 70% of serious flying incidents to human error, frequent flyers can take comfort in knowing that it is also humans that have plucked passengers from various pickles. Working on that mercurial human factor is the key to saving lives. As Wilbur Wright presciently penned in a letter in 1900: “What is chiefly needed is skill, rather than machinery.” He concluded: “It is possible to fly without motors, but not without knowledge and skill.”

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