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I've been watching this flight after they declared a general emergency and now they are following this oval flight path. Why would that be?

enter image description here

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    $\begingroup$ `cos flying in squares is difficult, and triangles is impossible. $\endgroup$
    – Criggie
    Commented Apr 13 at 12:51
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    $\begingroup$ @Criggie Well, ... npr.org/sections/thetwo-way/2017/08/04/541595580/… $\endgroup$
    – Ralph J
    Commented Apr 13 at 14:59
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    $\begingroup$ @ralphJ Well now, that's just showing off ! $\endgroup$
    – Criggie
    Commented Apr 13 at 23:18

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That track is a holding pattern. Aircraft fly in a holding pattern most commonly in busy airspace, to create a gap between them and other aircraft in front.

This particular flight is probably flying in the holding pattern while they troubleshoot the technical problem, or to burn off excess fuel to get to a lower weight, or simply to give the pilots time to get ready for landing. A holding pattern is much better than just flying in a straight line and going far away from the airport.

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An aircraft cannot just stop in flight, like a car stopping on the roadside. So when it needs some delay the crew flies this pattern, called a holding pattern, consisting in flying a leg of about 2 minutes, flying back and repeating as long as required.

In this case it was a Boeing 737-800 from Egypt Air, registered SU-GCM. As you saw it was squawking 7700 (emergency) after an engine failure.

From Aviation Herald:

the crew stopped the climb, initiated a descent and entered a hold.

They needed time perhaps to perform the emergency checklists, assess the situation and decide with the operator management the best option for the flight.

We don't know yet the cause nor whether the crew was able to restart the engine. After an engine shutdown and a successful restart, there is this checklist item:

Run the engine for three minutes at idle thrust

They decided to return to their airport of origin.

enter image description here

Source: FR24.

It took off again a few hours later.


Holding pattern

From SKYbrary:

Holding patterns are flown as a delaying tactic,

  • be it for ATC requirements such as airspace saturation or approach delays,
  • as the published termination of a missed approach procedure to be flown whilst coordinating further clearance,
  • at pilot request to allow time for completion of abnormal or emergency checklist procedures or at any other time that a delay in flight progress is required.
  • Under Instrument Flight Rules (IFR) pilots are expected to adhere to proscribed holding procedures inclusive of speed, hold entry procedures, timing and rate of turn, as the protected airspace for the holding pattern, and thus separation from other traffic, is predicated on those procedures.

Holdings ("stacks") are often seen near busy airports, e.g. see this animation from NATS, the ATC service in UK:

enter image description here

Engine failure

Losing an engine is not catastrophic, there is another one able to power the aircraft safely. But as a second failure would be a real emergency (not necessarily fatal), the crew must stop the flight and land, preferably at an airport where the engine can be checked and repaired.

A failed engine shouldn't be a cause of worry for passengers. The probability the second engine fails is tiny. E.g. twin-engine aircraft are allowed to fly without any airport available in a radius of 3 hours if the operator can demonstrate an average in-flight failure rate smaller than 0.02 per 1000 hours. With such rate the probability to have a dual failure within a period of 4 hours is $\small 6.4 \times 10^{-9}$ (thanks to @mbrig for fixing my calculation) compared to $\small 7.2 \times 10^{-9}$ for winning a typical lottery.

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  • $\begingroup$ @mins I not sure it matters much in terms of "valid degree of worrying" for the passengers whether the causes are independent or correlated. Though I think most of them will manifest pretty quickly, so I guess we can say that if the second engine holds out for 10+ minutes (?) you are probably not a victim of something that will affect both. $\endgroup$
    – mbrig
    Commented Apr 12 at 20:12
  • $\begingroup$ If we're going to get into the statistics philosophy though... once one engine has failed, we can't say the probability of a dual failure is (single failure)^2 any more. The chance the second engine fails is the same as it was before, 0.02 per 1k hours... $\endgroup$
    – mbrig
    Commented Apr 12 at 20:17
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    $\begingroup$ @mbrig Note that once an engine has failed there is no squaring any longer! Additionally, there are reasons to assume that there is an underlying reason that may affect the second engine equally (e.g. fuel issues, unreliable model, shoddy maintenance, end-of life or end-of service interval). Therefore, the probability for the second engine to fail as well may be much higher than the across-the board mean probability for any engine. $\endgroup$ Commented Apr 12 at 22:20
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    $\begingroup$ You'd think there would simply be a list somewhere, of, all cases of both-engine-failure last year. $\endgroup$
    – Fattie
    Commented Apr 13 at 12:16
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    $\begingroup$ 'deadstick_landing isn't necessarily fatal' ("with a glide ratio of 15:1, a Boeing 747-200 can glide for 150 kilometres (93 mi; 81 nmi) from a cruising altitude of 10,000 metres (33,000 ft).") $\endgroup$
    – Mazura
    Commented Apr 13 at 21:49

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