Air India Crash: Update #3

This is another update to my article Air India Crash: When 2 + 2 Does Not Compute with fresh evidence and arguments.

Many people assume, wrongly, that the chance of two identical engines losing power at the same time due to a component or systems fault must be billions to one.  Such occurences are indeed rare, but they do happen.

Deja Vu - A Warning About Possible Twin Engine Rollback At Takeoff

In 2009 there were two Boeing 777 incidents which resulted in no damage or injury, hence they did not gain much public attention.
Investigations found that the two cases in which there were single-engine thrust reductions during takeoff were the result of a software algorithm in the Full Authority Digital Engine Control (FADEC).
FlightGlobal1
In 2009 the FAA issued a directive which required revising the airplane flight manual to prohibit takeoffs at less than full-rated thrust.  That directive was partially superceded by an FAA directive requiring a modification to the FADEC software to prevent dual engine rollback at takeoff.


FAA AD 2006-20-51 R1AD 2006-20-51 R1 screen grab
We are issuing this AD to prevent dual-engine thrust rollback during the takeoff phase of flight, which could result in the airplane failing to lift off before reaching the end of the runway or failing to clear obstacles below the takeoff flight path.
FAA2
The key part is repeated as a quote for emphasis.  This FAA AD provides proof that in January 2009 it was a known fact that a FADEC software fault could cause a dual engine shutdown on takeoff.
This AD results from a report of two occurrences of engine thrust rollback during takeoff.
We are issuing this AD because the unsafe condition described previously is likely to exist or develop on other products of the(se) same type design(s) that could be registered in the United States in the future.
FAA2
It is of no significance that this FAA DA concerns the 777 and that the Air India tragedy involved a 787.  A FADEC is a computer which is programmed to optimise the fuel-air ratio depending on pilot thrust demand, altitude, air density, engine temperature, oil pressure and temperature and many other factors.  The FADEC is also responsible for engine protection against damage which might be caused by operation outside of the designed parameters.

Obviously FADECs are designed and programmed to match the engines with which they are to be used.  But it would be a specious argument to say that FADEC problems on other aircraft have no bearing on what happened to Air India 171.

Other Previous FADEC Problems

Mention was made in the original article of the 1995  Chinook and 2015 Airbus crashes due to FADEC malfunction.  The Chinook crash was originally put down to pilot error but subsequent inquiries showed that this Chinook was known to be unsafe due to multiple FADEC problems.

Mention was also made of a 787 dual engine shutdown on touchdown at Osaka.  That information is repeated here for the reader's convenience.

Uncommanded 787 fuel cutoff at Osaka3.

In 2019 an All Nippon Airways (ANA) flight touched down on the runway at which point the Thrust Control Malfunction Accommodation System malfunctioned and cut the fuel to the engines.

Uncommanded fuel cutoff Air Baltic Airbus A220-300

On 11th of July , the aircraft was carrying out a flight BT-139 from Riga - Latvia (RIX) to Copenhagen-Denmark (CPH), without any apparent issues throughout the flight.

While making an attempt to land on Copenhagen's runway 04L, both the GTF engines shut down automatically on touch down, with out any physical damage to the aircraft or injuiries to the occupants .

Though both the engines were out, cockpit crew could manage the control of the aircraft with a high speed taxi- out of the Runway. On stoppage of the aircraft, it was further towed away to a remote bay
fl360aero.com4
The FAA was notified of an airplane that experienced an uncommanded dual engine shutdown upon landing, resulting in compromised braking capability due to the loss of engine power and hydraulic systems. A subsequent investigation determined that the sequence of the auto-throttle increasing throttle to maintain Mach number, immediately followed by pilot command to decrease throttle to idle, caused a transient disagreement between actual and commanded thrust. This disagreement triggered the thrust control malfunction (TCM) detection logic and resulted in dual engine shutdown once the weight on wheels signal was activated upon landing. The installed EEC FADEC software version latches the fault and allows the engine to continue operation as commanded but shuts down the engine upon landing.
Federal Register5
Fly-by-electronics problems

When a plane's flight control, engine control and thrust malfunction electronics packages are interconnected then a simple transducer or coding error can cause problems if not predicted.  For example: the water ingestion testing of engines had to be modified because the results of melting hail had not been considered.  Testing and the engine design were both modified after a brand new Boeing 737-300 suffered flameout in both engines6 while descending through a severe thunderstorm.

Airbus flight-control computer software malfunction

Obviously the Airbus software is not the same as Boeing's software, but the principles involved in the programming are the same.  What happens to an Airbus can happen to a similar Boeing, and vice versa.  Remember the old adage: if it can happen it will happen.
Airbus A220 Software Update
The current software exhibits design flaws causing false rudder, aileron, and spoiler failure alerts through remote electronic unit transmission errors. Technical analysis reveals inadequate built-in testing protocols and monitoring systems.
Aviation A2Z7

Sources

1 - FlightGlobal
https://www.flightglobal.com/emergency-airworthiness-directive-issued-ov...

2 - FAA EASA_AD_US-2006-20-51R1_1
https://ad.easa.europa.eu/ad/US-2006-20-51R1

3 - 2019 All Nippon Airways (ANA) flight fuel cutoff
https://www.financialexpress.com/business/airlines-aviation/ai-171-crash...

4 - Rare Incident - 2.3 Years Old Air Baltic A220 Aircraft Suffered Automatic Shut Down ...
https://fl360aero.com/detail/rare-incident-2-3-years-old-air-baltic-a220...

5 - Airworthiness Directives; Pratt&Whitney Turbofan Engines
https://www.federalregister.gov/documents/2022/10/25/2022-22761/airworth...

6 - TACA Flight 100 - the plane that landed on a levee
https://en.wikipedia.org/wiki/TACA_Flight_110

7 - Airbus A220 Software Update
https://aviationa2z.com/index.php/2024/10/24/airbus-a220-software-update...

In preparation -
edit - added links
Air India Crash: When 2 + 2 Does Not Compute
Air India Crash: Update #1
Air India Crash: Update #2 - The AAIB Report Revisited
Air India Crash: Update #3
edit - corrected link to FAA AD re dual engine rollback