SpaceshipTwo accident pilot error?

Just read an interesting item on the BBC where the accident investigators detail the timeline of the tragic events. Highlights added by myself.

The vehicle, he said, was dropped from its carrier aircraft, WhiteKnightTwo, at an altitude of almost 50,000ft at 10:07:19 US Pacific time.

The ship's hybrid rocket motor was then ignited just a couple of seconds later, at 10:07:21.

Eight seconds after that (10:07:29), the vehicle was travelling just under the speed of sound (Mach 0.94). Two further seconds into the flight (10:07:31), it was travelling at Mach 1.02.

It is in that period between Mach 0.94 and Mach 1.02 that Michael Alsbury is seen on recovered cockpit video moving a lever to unlock the feathering system - an action that in the pilots' checklist was not called for until the vehicle had reached Mach 1.4.

However, and somewhat contradictory, the article then says

Investigators have previously described how the feathering system then deployed, apparently "uncommanded" by the pilots. It is probable that aerodynamic forces deployed the mechanism, resulting in the break-up of the ship. This is timed at 10:07:34 - the moment video and telemetry was lost.

So, are they hinting at a potential co-pilot error?

a reply to: MarsIsRed

Yes and no. It was pilot error that they unlocked the feathers too soon, yes. BUT, the feathers shouldn't have moved uncommanded the way they did. So THAT part was mechanical in nature.

a reply to: Zaphod58

So the correct order of events would be:

1) Unlock feathers, awaiting move command (but feathers stay put)
2) Command feathers to move

with the failure occurring between the two (presumably because of aerodynamic stresses)?


Edit: the reason I queried this was it was unclear whether the new information augmented or replaced the previous assessment.

a reply to: MarsIsRed

Correct. It's a two part deployment. They unlock them with one handle, usually at Mach 1.4. Then they stay retracted, and when they're ready to deploy them to slow down, they pull a second handle, and that deploys them. They're not supposed to be able to extend without being commanded to, but in this case they did. Mach 1 is when the most stress is on the airframe, and apparently it was able to deploy them, because of that stress.

a reply to: Zaphod58

Why would "unlocking" the feathers even be on the checklist while the motor is still burning?

I'm sure they are going to change that procedure.

I understand the Mach 1 stresses required the shuttle to throttle down briefly (high speed & high air density), so nothing new there.

But, this sounds like an avoidable accident had the lock been kept in place until Mach 1.4. At least potentially - of course there may be other information we're not privy to at this point.

a reply to: intrptr

In case there's an emergency and they need to slow down. Once at Mach 1.4 or higher, then the stress is significantly reduced on the airframe, and there is almost no chance of them deploying unintentionally.

a reply to: Zaphod58

…and there is almost no chance of them deploying unintentionally.

They'll still change the procedure. Because it did happen.

a reply to: intrptr

No, most likely they'll build a safety backup into the system that will keep it from happening again. They went with a procedural system, instead of a physical interlock it seems, other than the handle. Now they'll most likely redesign it with something so that even if they unlock it, it can't physically move unless the other handle is pulled too.

a reply to: Zaphod58

Now they'll most likely redesign it with something so that even if they unlock it, it can't physically move unless the other handle is pulled too.

More handles to pull in case of emergency?

I wanted to say that should be a computer driven thing but they don't have NASA's unlimited budget.

Just sounded weird "getting ready" to feather while still burning.

Dragsters wait to deploy the chute until they take their foot off the gas. maybe there is a system already deployed there that is more "pull proof"?

a reply to: intrptr

They'll either install a mechanical interlock, that is controlled by speed, or a software interlock. My bet is on software though. It won't add any weight to the vehicle that way.

a reply to: Zaphod58

Query on this point, Zaph: say they do need to slow down due to some emergency and deploy the feathers. As you say, the stress on the airframe is less at Mach 1.4, but if they then feather to slow down, they'll assumedly reach Mach 1 -- where the stresses are highest. So, what's to stop the craft breaking up at Mach 1 under that situation? Would the difference be that they'd also throttle back at the same time and reduce stresses from thrust?

I'm also wondering if there is a fundamental flaw in the feather design if it can lead to airframe failure at Mach 1 under (almost) any circumstances.

I heard that the Feathering system is an automatic sytem, not controlled by the pilots, but by certain parameters during descent enable the feathering system to become operational. So then this would not be pilot error at all

originally posted by: Zaphod58
a reply to: MarsIsRed

Yes and no. It was pilot error that they unlocked the feathers too soon, yes. BUT, the feathers shouldn't have moved uncommanded the way they did. So THAT part was mechanical in nature.

The feathers deal with reentry correct?

If they are deployed for reentry would the process not be automated?

a reply to: JustMike

If they had to deploy them for an emergency, they'd also have the throttle down to almost zero, so the stress going back down through Mach 1 would be negligible.

a reply to: Glassbender777

Not entirely true. Yes, it's for reentry, but it's manually controlled by the pilots, through the use of two separate handles in the cockpit. One to unlock them, and one to deploy them. The first handle was pulled early on this flight, which unlocked them. The stress apparently then caused them to deploy.

a reply to: Zaphod58
Okay. In that case it makes sense.

Hope they figure exactly what went wrong.

originally posted by: Zaphod58
a reply to: MarsIsRed

Yes and no. It was pilot error that they unlocked the feathers too soon, yes. BUT, the feathers shouldn't have moved uncommanded the way they did. So THAT part was mechanical in nature.

It isn't necessarily pilot error that the feathers were unlocked too soon. There could be an instrumentation fault and the airspeed indicator the co-pilot was looking at indicated the vehicle was at the correct speed for feather unlock.

a reply to: nataylor

It could be, but then it still would be human error that they didn't see it. They should have been coordinating with the launch aircraft for release speeds, and noticed the disparity between the speed showing, and the speed being told them.

With this and the private rocket to supply the ISS blowing up -- why do I feel that perhaps a message is being sent to private space companies to "slow down"?

Just something in my gut that I've been feeling.