Caverton AW139 incident in Jan 2024
 

Summary: Loss of AP while airborne leads to unusual attitudes for several minutes in flight. Many unhappy passengers.

This looks like it was a bit exciting. Anyone have any insight as to if the correct procedures were followed?

https://nsib.gov.ng/wp-content/uploa...t_5N-BSG-1.pdf

The QRH states that following a single AP Fail

”- If subsequent 1-2 AP fail caution illuminates
- Continue flight manually not exceeding 140 KIAS (100 KIAS in turbulence,
IMC or approach)”

Nowhere does it mention resetting them repeatedly or shutting off the gang bar.

Anecdotally the 139 year would regularly drop APs, especially on approach and it wasn’t uncommon for the PM to “guard” the AP buttons on the AFCS panel for a quick attempted reengagement.

Nothing wrong with seeing if it will come back on. But 5 attempted resets followed by turning off both generators at the same time in flight via the gang bar is bizarre.

The 139 can be a handful without the APs but not 3000ft to 300ft in 45s, perhaps more time should be spent on training manual control of the aircraft with and without AP. Seems like subsequent loss of AP1 after messing around with the electrics wasn’t expected followed by panicked over controlling.

Megan, I think Nescafe was referring to the QRH not mentioning resetting the Gangbar. The report clearly states that's what the crew did.

Thanks all for the information. Sounds like a major mishandling of the aircraft then.

It’s always ok when everything works, but simple failures offered in the sim result in the most bizarre behaviours in my experience ( as a former TRE on the 139 ), some would have me tightening the seatbelt even… 🤭

The Preliminary Report makes disturbing reading. The two pilots seem utterly preoccupied in keeping the autopilots engaged, and repeated pressing of buttons seems to be their preferred course of action, during which the aircraft is all over the place:

The 'Initial Findings' section of the Prelim report states "8. The serious incident occurred in Instrument Meteorological Conditions (IMC)." The preoccupation with autopilot engagement (never mind the 45 second dive from 3500 ft to 330 feet!) leaves me with a distinct impression that the pilots were very reluctant to manually fly the aircraft! Is that because they are not confident about doing so in IMC, perhaps rarely practising doing so?

A few more items of interest from 'Initial Findings' section of the Prelim Report:

Additionally, "The aircraft sustained minor damage.":

Yes, I can sympathise with that. 😲

I am in no way defending the crew's actions but, when discussing manual flying, I think it's worth remembering that having turned off the generators they were left with standby instruments only and zero stabilisation (in IMC), so it was a bit more complicated than simply hand flying. Nonetheless, pretty astonishing to have been out of control for that length of time. I find the crew's actions in making non-standard interventions, resulting in a loss of control, reminiscent of the AirAsia accident a few years ago: https://en.wikipedia.org/wiki/Indone...ia_Flight_8501
It will be very interesting to see the final report and more data on the flight trajectory. Anecdotally I have heard they fell out of the cloud base at 1500 ft doing 13,000 ft/min (7 seconds to impact) and pulled 4g in the recovery!

EDIT - I am hearing from a friend that when you move the electrical gangbar it takes out the battery too, so also the standby instruments (an integrated EFIS). So, even when you realise your error and reset it, everything has to power up, go through their BITs etc and come on line. So, unstabilised in IMC with no instruments - sporty!

Can any 139 pilots confirm?

The 139 was developed and marketed as a fully PC1 aircraft, including procedures and profiles to deal with that dreaded single engine failure.
On approach, the profile will settle you in a high vibration regime that could kick the AP's off. If you'd flown a 500 and instinctively minimized time in paint-shaker mode you'd be up in front of the FDM board explaining why you deviated from the PC1 profile.
I don't know Caverton's training, but likely focussed on engine failures (PC1 myopia). Not much time left over for AP's off, or standby instrument recovery from IMC. Not much different in the rest of the world.
I flew for a large operator that would regularly do both AP off training in the 139 aircraft, as did the factory. I noted other operators prohibited their training staff from doing this, citing a POH limitation.
Nothing like lifting off a deck at night with both AP's still off ....

I recall another highly-feted Nigerian crew ditching an S76 offshore after forgetting the AP's and deeming the aircraft too unstable to fly. Limited training time, focus on what the regulator wants to prioritize. In another case a droopy-eyed expat lost it in cloud between the beach and PH, saved by his sharp Nigerian national copilot.

Not quite - left the compasses in DG then the AP didn’t behave as they expected. But, hailed as heroes in the local press

Seems like they may not have had any instruments for a bit - see my last post.

From the AW139 Technical Notes

”Red Gang Bar moved backwards cuts off all aircraft electrical power sources at the same time. (Gen 1 & 2 and Battery Master switches are moved to OFF all together.)”

The Battery Master switch needs to be on to enable the Main and Aux to be connected to Main Bus 1 & 2.

Thanks - seems to corroborate my info. So, given that most AHRS normally take about 30” to come online when sitting on the ground motionless, and a minute or two in flight, or on a moving deck, one can imagine that they take a bit longer while doing aerobatics!

Just FLY the damn chopper! Or have we forgotten how???

I don't think anybody would argue with that sentiment, but it's not clear what phase of this event you're referring to? With the AP drop out, then of course fly the aircraft and follow the QRH - which says decouple the Flight Director, ergo fly manually with the remaining AP in ATT mode. Some OEMs say try to attain VMC, but I see the 139 QRH does not say this. It does say that if the other AP fails then reduce speed to below 100 KIAS, and it also says (in the limitations section) that taking the APs out of ATT mode in IMC is forbidden.

However, from what we are now learning, the captain used the electrical gangbar, which turned off all the electrics at once, leaving them with no flight instruments at all, and a totally unstabilised aircraft which, I am sure, would have rapidly departed normal flight. Even with the electrics restored immediately, there would not have been any usable attitude information for quite some time, so the concept of "just flying the damn aircraft" is a bit moot at this point - they were essentially passengers. I think that had the cloud base (which gave them the visual references for recovery) been much lower this would have been a fatal accident.

Caverton has a Level D FFS in their main base, so it would be very interesting to see how this event looks like replicated in there! No doubt, that has already happened....

A graphic example of why it is a very bad idea to make up your own drills or actions. Thank goodness that all survived this, with only minor damage to their underwear.

This gang-bar reset thing sounds as if the Captain had done it before, but didn't think about the battery also going off and losing the standby instruments - I mean who would intentionally switch off ALL electrical sources in flight, unless the actual published QRH or published memory drill demanded it ?

Out of interest; what caused the windows to smash in this incidence ?

If during Non SAR mission
- Continue flight attentive do not exceed Vne-27 KIAS in level flight, or 100 KIAS and 1000 fpm in climb.
- Decouple FD (below 500 ft (152 m) AGL fly manually) unless in approach, missed approach,AFCS approach and departure to/from hover and hover

As another pprune user usually says, just start the clock and don't touch anything... :}

I have an old uncontrolled copy that has similar but slightly different wording - thanks for the update.

​​​​​​​My assumption is either fuselage flexing, or extreme side-winds, but just a guess.

It could have been the passengers, looking for a way out.

Wouldn't you consider it if you were down the back?

To get out on the ground, possibly if the door didn't open and getting out was imperative. But there was no reason to exit in an emergency, was there ?

For some reason, I thought they meant the windows had smashed in flight somehow.

Interestingly this recently cropped up in the sim ( unrelated ) and - as stated - the gangbar shuts down everything and takes about 30 seconds for everything to reboot during which time the aircraft could do anything. In this case the aircraft was recoverable but was in a very unusual attitude when the lights came back on.............. Turning everything off ON THE GROUND was an unofficial engineering CTR ALT DEL to clear snags otherwise requirering a shutdown etc etc. It was never recommended to crews and certainly not in flight...

Nagging question for 139 experts - how was the FDR recording the flight parameters after the power was cut? I can imagine it was powered up immediately after the gangbar use, but what about the data?