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An American Airlines mechanic sabotaged a 737 in Miami

An American Airlines mechanic accused of sabotaging a navigation system on a flight with 150 people aboard at Miami International Airport was denied bond by a federal judge on Wednesday after prosecutors suggested he may have links to a Middle East terrorist organization.

Abdul-Majeed Marouf Ahmed Alani, a 60-year-old veteran employee, told investigators after his arrest earlier this month that he disabled the system because he was upset over stalled union contract negotiations with the airline and wanted to generate some overtime for maintenance on the plane. He said he meant no harm to anyone, and the July 17 flight was aborted before takeoff after an error alert appeared on the navigation system.

His defense attorney said it wasn't as big a deal as they were making it out to be

But Alani’s assistant federal public defender, Christian Dunham, said the prosecutors were exaggerating the evidence. He pointed out that there was a second navigation system still working on the plane so his alleged sabotage could not have caused it to crash.

“We don’t believe he intentionally endangered the safety of people” on that flight, said Dunham, who sought a pretrial bond signed by Alani’s family members in California and Florida. “I think the government is blowing this out of proportion.”

What was it he sabotaged, and how serious would it have been if it had taken off?

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    $\begingroup$ I'm not experienced enough to answer this formally but the assertion by the defendants lawyer that "there was another system" is absurd and dangerous. They went from two systems to one. That reduces the margin of error and is still dangerous. I don't quite know the stats and the lingo here, can an answer include some remarks on this? $\endgroup$ – Freiheit Sep 20 at 14:42
  • $\begingroup$ Couldn't agree more with @Freiheit. Everyone deserves a defense; the public defender in question should be given a medal for the most astonishing, astounding, spectacular line of b/s of the year. $\endgroup$ – Fattie Sep 23 at 10:35
  • $\begingroup$ @Freiheit Assuming the mechanic had the opportunity to disable both systems, the fact that he only disabled one could indicate his intent wasn't to make the plane crash. $\endgroup$ – JollyJoker Sep 23 at 11:42
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It's a serious crime, but what that guy did, only affecting one system out of three, would be unlikely to cause a crash if the pilots were half way reasonably competent. The take-off would be rejected as soon as the blocked side's speed tape failed to "come alive", well below 80kt (the pilot not flying checks that both speed tapes start to move as the airplane accelerates - this would be the first obvious clue and is a very basic action on a jet).

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    $\begingroup$ In fact, the article quoted in the question says that the takeoff was aborted because the damage was detected. $\endgroup$ – Barmar Sep 20 at 17:20
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    $\begingroup$ It actually says the flight was aborted before takeoff. That's different from the takeoff was aborted, and could be also interpreted as cancelled.. $\endgroup$ – Michael Hall Sep 20 at 19:09
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    $\begingroup$ I downvoted because the statement "would be unlikely to cause a crash if the pilots were half way reasonably competent" is overly judgmental and I think, incorrect. Unreliable airspeed in flight is a serious problem, and not terribly easy to deal with. I agree with you that it shouldn't cause a crash, but it has caused crashes in the past. Further, the idea that "if they accelerate to 80, detect a mismatch, and abort, it's safe" is also wrong, aborts above 80 kias are considered high speed, and are not only moderately dangerous, but also often result in damage to the aircraft. $\endgroup$ – nexus_2006 Sep 22 at 18:39
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    $\begingroup$ @nexus_2006 I said "well below 80kt" (or 90 or whatever) The tape moves long before 80kt so it would be a low energy reject. It's something that's done regularly in the sim on recurrent. Verifying speed alive, on BOTH sides, is Job #2 for the pilot monitoring after verifying engine parameters after thrust set. Now, if the PNF wasn't, you know, doing his/her job and paying attention, and called airspeed dead just before V1, well we're back to the halfway competent thing aren't we. $\endgroup$ – John K Sep 22 at 18:59
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    $\begingroup$ It's utterly astounding to try to "softly defend" some fool who turned off a major system on an airliner. $\endgroup$ – Fattie Sep 23 at 10:33
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According to BBC's description, he blocked one of the pitot tubes.

(...) a piece of foam was found glued inside a navigation system part which stopped it from functioning. It was reportedly inside the tube leading from the outside of the plane to its air data module, a system that reports aircraft speed, pitch [sic] and other critical flight data.

A blocked pitot is very serious. One blocked pitot caused the crash of Birgenair Flight 301 after takeoff, for example.

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  • $\begingroup$ On the other hand, I would be very disappointed in pilots who cannot fly the plane with all pitot tubes completely blocked and reading 0 airspeed. $\endgroup$ – Joshua Sep 21 at 3:21
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    $\begingroup$ Yes, you would be rightfully disappointed if the pilot didn't detect the dangerous tampering, but then you might be dead. $\endgroup$ – gnasher729 Sep 21 at 13:15
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    $\begingroup$ Serious, yes, though a single pitot tube being blocked is readily detectable. IIRC, in Birgenair 301, the ASIs disagreed already during the takeoff roll; Wikipedia appears to agree. $\endgroup$ – a CVn Sep 21 at 14:22
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    $\begingroup$ @Joshua A blocked pitot tube doesn't cause a zero airspeed indication. Rather, it causes the ASI to function as a crude altimeter (showing an increase in airspeed as the aircraft climbs), which very likely contributed to the pilots' confusion on Birgenair 301. See What does the Airspeed indicator show when your pitot tube is blocked? $\endgroup$ – a CVn Sep 21 at 14:30

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