A Jet Airways flight coming in to land in Mumbai in October lost height faster than the prescribed rate of descent as the auto-pilot tripped, the flight director disappeared and the ground-proximity warning system went off.
The dangerous turn of events began — about 3,700 feet above the ground — when a check pilot, seated behind the commander and the first officer on the Jet Airways Delhi-Mumbai flight, pulled out a circuit-breaker.
He did it ostensibly to check the pilot’s ability to handle an emergency. Only, such checks are always done in simulators — never with a plane load of people.
Jet Airways has ordered a probe, but it has not derostered the check pilot though both aircraft manufacturers Boeing and Airbus have a strict policy warning flight crew against use of circuit-breakers during flight — they are not pulled even on a check or a test flight.
So, with both vital navigation instruments failing, the commander took over the flight controls to bring in the plane for landing entirely manually. “But the aircraft started sinking fast. It was going down faster than 1000 feet a minute, the maximum prescribed descent rate. It was a dangerous situation as the approach to runway 27 was over hilly terrain,” the official said.
“Since the sink rate was very high, the Digital Flight Data Recorder showed up an `exceedance report’, which was picked up by the airline’s flight safety department after the aircraft landed,” said the source.
“It is a very dangerous thing to do as pulling out a C/B can render unintended systems to fail, like the EGPWS failure in this case. No pilot would want to fly without an EGPWS,” an official said. Aircraft manufacturers are so careful about C/Bs that these switches are not installed at locations easily accessible or even viewable from the pilot’s seat. It is located behind the seat as Airbus and Boeing did not consider the possibility of an ACM pulling out a C/B.
Source: The Times of India
By: Whiskey Delta - 6th December 2009 at 02:09
Wonder if some how the aural warning system was killed in the process. If it wasn’t working, or working right, the crew might not have realized the A/P was offline.
By: Arabella-Cox - 5th December 2009 at 17:01
Yes, strange if they were on a stabilized approach…was it an Airbus? Are there any Airbus experts who know what that CB is for?
By: Deano - 5th December 2009 at 15:34
27vet, even if they were slow to react they wouldn’t lose more than 50-100ft. We are very often out of trim when disconnecting on the ILS, this is because when you disconnect you should do it when the plane has “settled” and is not chasing the Glideslope. I cannot see that 2 pilots would be slow to react, because the jolt it gives you wakes you up in a split second.
By: Ren Frew - 5th December 2009 at 14:20
Interesting replies fellas.
By: Arabella-Cox - 5th December 2009 at 13:58
You reset a CB once and if it trips off again you leave it like that and follow the emergency or abnormal checklist, usually select a backup service in that case. And one CB should not protect both an essential service and its backup. But there is more to this incident than meets the eye. Failure of the EGPWS and disconnecting the autopilot should not cause the plane to lose height unless it was out of trim and the crew was slow to react.
regards
Ralph
By: Whiskey Delta - 5th December 2009 at 06:23
They aren’t removeable. They basically are push to reset buttons that can be manually pulled to deactivate a system if needed for maintenance reasons. It isn’t a good idea to pull a CB in flight as you’d be hard pressed to know for 100% what systems will be deactivated. For that reason pulling CB’s only done on the ground when such actions have little consequence should something unexpected happen.
CB’s for the most part are visible by the crew as it’s one of the first placed you look should a system go off line. If system C stops working and you notice the CB for that system has tripped then you know an electrical spike of some kind took it off line. In some instances it might be prudent to reset the CB to see if the system goes offline again in case it was an electrical anomoly the first time.
By: Ren Frew - 5th December 2009 at 01:33
Aircraft manufacturers are so careful about C/Bs that these switches are not installed at locations easily accessible or even viewable from the pilot’s seat. It is located behind the seat as Airbus and Boeing did not consider the possibility of an ACM pulling out a C/B.
Might I enquire as to why circuit breakers are hand removable at all then ? Surely the literal equivalent of the comedic, big red ‘do not touch’ button ? :confused:
By: Whiskey Delta - 5th December 2009 at 01:23
One question though, what happens if the circuit breakers break of themselves. It sounds like the pilots would hae a hard time replacing them when the concequences might be considerable.
As far as I’ve seen they aren’t replaceable and no replacements are stored in the cockpit.
By: Arabella-Cox - 4th December 2009 at 19:13
One question though, what happens if the circuit breakers break of themselves. It sounds like the pilots would hae a hard time replacing them when the concequences might be considerable.
You are right on that score!
By: tenthije - 4th December 2009 at 17:53
I can’t believe the check pilot was not put on non-active for this stunt.
One question though, what happens if the circuit breakers break of themselves. It sounds like the pilots would hae a hard time replacing them when the concequences might be considerable.
By: Arabella-Cox - 4th December 2009 at 17:37
Might be a good reason to install cockpit cameras. Imagine if they had crashed. No-one would have known what really happened.
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December 4, 2009 at 12:33 am