NTSB Meeting on SpaceShip Two Accident

[Vinny]

NTSB met July 28 to discuss the SpaceShip Two Accident. Meeting materials:
http://www.ntsb.gov/news/events/Pages/2015_spaceship2_BMG.aspx

Abstract of the meeting, including probable cause statement:
http://www.ntsb.gov/news/events/Documents/2015_spaceship2_BMG_abstract.pdf

The National Transportation Safety Board determines that the probable cause of this accident was Scaled Composites’ failure to consider and protect against the possibility that a single human error could result in a catastrophic hazard to the SpaceShipTwo vehicle. This failure set the stage for the copilot’s premature unlocking of the feather system as a result of time pressure and vibration and loads that he had not recently experienced, which led to uncommanded feather extension and the subsequent aerodynamic overload and in-flight breakup of the vehicle.

Also, Parabolic Arc posted stills taken from the SS2 tailboom camera used in the NTSB's investigation, along with (hard to read) annotations by the NTSB:
http://www.parabolicarc.com/2015/07/29/breakup-spaceshiptwo-frame-frame-tail-boom/

 

[frcabot]

I thought there was discussion earlier on that the copilot mistakenly unlocked the feather system but didn't deploy it, and that the extension was uncommanded.

Edit: yes, that's what it says. If so, isn't the bigger problem the uncommanded extension rather than the unlocking? The unlocking should have had no effect whatsoever.

 

[Ken Ibold]

I thought there was discussion earlier on that the copilot mistakenly unlocked the feather system but didn't deploy it, and that the extension was uncommanded.

Edit: yes, that's what it says. If so, isn't the bigger problem the uncommanded extension rather than the unlocking? The unlocking should have had no effect whatsoever.

I haven't read this report, but my understanding was that the uncommanded extension was due to aerodynamic forces as the supersonic shock wave propogated along the fuselage.

 

[nauga]

Edit: yes, that's what it says. If so, isn't the bigger problem the uncommanded extension rather than the unlocking? The unlocking should have had no effect whatsoever.

The "big" problem was that unlocking the feather early, a single event, set up an irreversible chain of events that would result in catastrophic failure, and that the systems-level testing up to that point did not take human error (other than delayed pilot reaction) into account as is required by the FAA.

Nauga,
who has followed the same path to a different destination

 

[frcabot]

The "big" problem was that unlocking the feather early, a single event, set up an irreversible chain of events that would result in a 'catastrophic event,' and that the systems-level testing up to that point did not take human error (other than delayed pilot reaction) into account as is required by the FAA.

Nauga,
who has followed the same path to a different destination

Ok, but unlocking the feather should not have resulted in an uncommanded deployment, resulting in a catastrophy. So aren't we saying the same thing?

nauga,
who has really annoying signatures

 

[nauga]

Ok, but unlocking the feather should not have resulted in an uncommanded deployment, resulting in a catastrophy. So aren't we saying the same thing?

Are we? Unlocking the feather resulted in deployment. They either knew or strongly suspected this would happen, which was why they put the manual lock in. The failure they experienced should not happen in a 'safe' design but was going to happen per the then-current SS2 design if the lock was unlocked early - as it was.

Note: This post is certainly a reflection of my opinion but it's fairly well substantiated by the contents of the accident docket.

Nauga,
and his FMECA

 

[frcabot]

Are we? Unlocking the feather resulted in deployment. They either knew or strongly suspected this would happen, which was why they put the manual lock in. The failure they experienced should not happen in a 'safe' design but was going to happen per the then-current SS2 design if the lock was unlocked early - as it was.

Note: This post is certainly a reflection of my opinion but it's fairly well substantiated by the contents of the accident docket.

Nauga,
and his FMECA

If they knew that unlocking the feather would result in an uncommanded deployment, then yes, that's a big problem.

Fmeca?

 

[Henning]

Ok, but unlocking the feather should not have resulted in an uncommanded deployment, resulting in a catastrophy. So aren't we saying the same thing?

nauga,
who has really annoying signatures

It wasn't uncommanded, it was commanded by the shockwave passing over it, that's why there was a lock on it.

 

[Henning]

If they knew that unlocking the feather would result in an uncommanded deployment, then yes, that's a big problem.

Fmeca?

Well, isn't that why the lock is installed?

 

[frcabot]

Well, isn't that why the lock is installed?

I would have thought it would have been to introduce an additional layer of safety, in other words a redundancy, not a single failure point.

 

[Henning]

I would have thought it would have been to introduce an additional layer of safety, in other words a redundancy, not a single failure point.

You can't build anything mistake proof, especially not when you are weight conscious.

 

[frcabot]

You can't build anything mistake proof, especially not when you are weight conscious.

With computers and computer locks I'd think it'd be a lot easier. It doesn't necessarily have to be a mechanical redundancy. Just design the pilot out.

 

[Henning]

With computers and computer locks I'd think it'd be a lot easier. It doesn't necessarily have to be a mechanical redundancy. Just design the pilot out.

Money and weight. Might as well get rid of the pilot altogether and have an autonomous payload hauler. Just remember a commuter control lock can fail as well.

 

[frcabot]

Money and weight. Might as well get rid of the pilot altogether and have an autonomous payload hauler. Just remember a commuter control lock can fail as well.

Computers and adaptive robot