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Shutting Down an Engine Mid-Flight

Q: But, to think outside the box for a moment, why not shut down an engine? If a four-engine plane can fly just on three, or even two, why not put one to sleep for a few hours over the ocean?

During flight, the repercussions of a shut-down engine are vastly different than on the ground, affecting everything from cruising speed to altitude to pressurization. While perfectly able to compensate for one another in the event of inflight failure, engines not designed solely in the interest of redundancy. They work together.

For example, losing an engine over the ocean, seldom as it happens, typically mandates a reduction in speed and descent to a lower altitude. High altitudes mean thinner air, and you need more available power to cruise there (certain aerodynamic issues also come into play.) And once the speed/altitude variables shift, so do those of range — to the intended destination and to any required diversion points.

In other words, an expired engine requires recalculation of the entire flight plan. Even with four engines this can mean a midflight detour (hello Keflavik, or Anchorage). Not because the plane is on the verge of crashing, but because all of the range and performances parameters have shifted. The demanded descent and other aerodynamic penalties increase fuel consumption, and may in turn require even more fuel than is “saved” by the dead motor.

This was illustrated wonderfully in late February, when a British Airways 747 headed for London lost one of its four Rolls-Royces shortly after takeoff from Los Angeles. In a move that garnered press attention and sparked something of a furor, the crew pressed on for England rather than return to LAX. An unorthodox decision, and, to go on the record, not one I’d endorse myself, but perhaps not altogether stupid or dangerous, considering the 747’s capabilities on three, or even two engines, and the extreme improbability of a second failure. After running the numbers, it was determined the flight would have sufficient fuel to continue safely.

“That’s not something our own company would have allowed,” says Michael [last name withheld], a 747 first officer with a major US airline. “But in a way I can sympathize, and it’s not as crazy as it probably sounds to the layperson.”

Pilots do not make such critical decisions entirely on their own. Crews work in concert with an airline’s dispatch department (known assortedly as flight following, flight control, and such), with whom they remain in contact for the duration of the journey, weighing the advice of various technical staff. That being said, ultimate and final authority rests with the captain. “You can be assured,” adds Michael, “no crew would have accepted the recommendation to keep flying had they thought the idea was unsafe.”

Was British Airways, with the captain’s blessing, acting on behalf of financial concerns? Partly, sure, but that in itself isn’t tantamount to recklessness.

Unfortunately, BA268 encountered lighter than expected tailwinds (that’s different from purported “stronger headwinds” as you’ll read elsewhere), and when the amount of remaining fuel began to fall below target values at en route waypoints, the captain realized a diversion to Manchester would be prudent. The fuel progress portion of a flight plan, amended or otherwise, can go on for several pages. Burn totals (actual versus that anticipated) are carefully crosschecked numerous times en route. The plane was not “running out of fuel,” as the Times so crudely put it. Less dramatic, but more accurately, the 747 would no longer have met the reserve buffer should delays or a holding queue have struck near Heathrow.

But that’s no fun for the Times, which prefers conjuring up images of a goggled aviator tapping on a gauge and exclaiming, “Yikes! We’d better put her down, mate.”

On Tuesday the affair made an appearance in Scott McCartney’s “The Middle Seat” column at the Wall Street Journal. I enjoy Scott’s work, but the affection may or may not be mutual now that I’m formally upbraiding him for repeated use of the annoying “British Air” bastardization. McCartney also states: “For US airlines, Federal Aviation Administration regulations require commercial carriers to land at the nearest suitable airport after an engine failure.”

This is only true for aircraft with fewer than three engines. Exemption 121.565(b) of the Federal Aviation Regulations allows the pilot-in-command of a three or four-engine commercial transport to continue onward, subject to a reasonable series of weather and fuel stipulations (though an airline’s in-house rules may trump the FARs).

McCartney goes on to write that flight 268 flew “up near the North Pole” as it hobbled to Heathrow. He has the right idea, but he’s a good thousand miles off course (magnetic or true, for those of you know the difference). Hasn’t he seen the Great Circle Mapper?

This Q&A is part of a collection that originally appeared on Patrick Smith, 38, is an erstwhile airline pilot, retired punk rocker and air travel columnist. His book, Ask the Pilot (Riverhead) was voted “Best Travel Book of 2004” by Patrick has traveled to more than 55 countries and always asks for a window seat. He lives near Boston.