RAT on Challengers

[hawker750]

RAT on Challengers






An N reg Challenger 60 something has been on maintenance at Biggin for a couple of months and as part of the check it was required to do a test flight to check the operation of the RAT. When it landed it burst all 4 tyres, wrote off 4 wheels and brake units. Apart from pissing off Biggin operators by closing the airport for a few hours what I would be interested to learn from you Challenger guys is:
1/ The RAT is supposed to be a safety system, how come it did not live up to it's name on this occasion?
2/ Apparently the maintenance organisation placed their engineers on board and as this check would have been part of the scheduled inspection who is going to take responsibility for this incident? Is it the maintenance organisation? They presumably could not issue a maintenance release until after the satisfactory outcome of this check so technically they still had the duty of care on their shoulders. Or was it the pilots?
Wherever the blame lies I guess the lawyers and Insurance companies will slug it out as I presume the bill will not be cheap.
IMO post maintenance test flights are often carried out with not enough forethought as to what can go wrong and all too often something does go wrong. The CAA have an excellent flight test department who are only too willing to come out and fly your aircraft on test flights. I recommend them, you will learn a lot and the last time I used them the service was free!

[BizJetJock]

The RAT is supposed to be a safety system, how come it did not live up to it's name on this occasion?
What a bizarre question. If you went up on maintenance test flight in your hawker to check the aileron rigging and the flaps failed, would you ask why the ailerons did not perform as per spec? :ugh:

[hawker750]

BJJ Your comment daft. If I went up to test my flaps and my flaps failed I would want to know why. What I am curious about is what happened? Guess have to wait for the official report, but is there a way the operation of the standby generator and switching off the main generators could produce this scenario?

[BizJetJock]

No my comment wasn't daft. You didn't ask "what might have caused this?", you asked "Why didn't the RAT (ADG) live up to its name?". You assumed that the ADG drop was directly related to the incident.
4 burst tyres and associated damage could be caused by enthusiastic braking with the anti-skid off, but the only way that would be related to the ADG drop would be if they failed to get any of the other 3 generators back online after the test. If that was the case you might have heard about multiple electric failures being a part of the incident.

[hawker750]

Thanks, I have been told this is what happened that they landed with only ADG powered and no other generators on line. Would this cause 4 tyres to burst?

[BizJetJock]

Standard advice is that any significant braking over 80kts without antiskid will burst tyres - I've never tried it for real!
If landing on ADG only then antiskid is not available, but Biggin is plenty long enough to land using only reverse and no braking at all at typical air test weights.

[josephfeatherweight]

I have conducted the airborne ADG deployment test a number of times in the 604. Personally haven't experienced any problems during the exercise. Must've been a problem with the power-transfer-override.

[BizJetJock]

Amendment to my last: if it was anything other than a 605, they would have to do a flapless landing on Emer Pwr only. In this case they shouldn't be landing at Biggin at all as the factored ALD is more than the runway available.
On the 605 they finally gave you one flap motor on the essential AC bus so you can use the flaps.

[Fossy]

They presumably could not issue a maintenance release until after the satisfactory outcome of this check so technically they still had the duty of care on their shoulders.

If the aircraft was accepted without a release to service, the aircraft was not airworthy, meaning the CofA would have been invalid during the flight. Therefore I've my doubts that the aircraft was not released to service. The RAT OPS check is a stand alone task and independent from other inspection tasks.

[x933]

One can't help but wonder that if you needed an ADG for real four burst tyres would be the least of your worries.

[Steak&Kidney_Pie]

RAT/ADG testing is a normal check on the Challenger series. Normally requested by the engineers before taking the aircraft in for major maintenance.

There is a full checklist provided, to ensure that you land with sufficient electrics to power the antiskid. Antiskid on the Challenger works down to 12kts.

Some great marks on the runway in Biggin upon landing yesterday....even better were the wheel rims......nicely flattened! Apparently a JETS engineer was onboard too!

[orion1210]

Rat drop procedure on 604/605 is fully supported by a FCOM in flight check procedure so can by conducted without any special flight release, although it does call for VMC. An engineering visual inspection prior to in flight deployment check is required on certain units, in which case normally prevents a drop on the way into mx.

If the event on landing was due to electrical issues, they possibly didn't restow the manual release handle which can apparently cause 'damage' to the electrical control system and/or prevent switching of the essential bus back to a gen prior to landing. During my involvement with this check, despite a pre-brief, i've often had to remind crews to restow the deploy handle even when they're running the list. I guess it gets lost in the awe of the RAT noise and unusual cas messages ;) I wouldn't be suprised if the procedure is revised to further reinforce this important step in the near future.

I'll be very interested in the investigation on this one.

[ksjc]

Have done many CL RAT drops through the years (601 and 604) and learned a few things. Super noisy, distracting, a bit chaotic and crew CRM goes out the window. Best to have a tech on the jumpseat working the checklist with the PNF to accomplish items carefully. Easy to miss a critical step in all the excitement.

PF manages the flying "single pilot" style (with full David Clark headset on) and this is one good reason there's a VFR only requirement.

Probably not the safest thing I do but it gets the job done every 2 years.

Regarding the OPs remark about tire blowout. The RAT wouldn't have caused that to happen but a badly managed RAT drop procedure might have.

[frontlefthamster]

The CAA have an excellent flight test department who are only too willing to come out and fly your aircraft on test flights.

Sadly no longer. The CAA had two test pilots, one was made redundant and the other resigned. I am informed that there are no plans to replace them.