SpaceShipTwo: Were Proper Communications Protocols Followed on Feather Unlock?
OK, everybody.
The NTSB just completed its final media briefing in Mojave on the SpaceShipTwo investigation. And this story got stranger.
During the Q&A, NTSB Acting Chairman Christopher Hart appeared to back off his claim yesterday that it was co-pilot Mike Alsbury, who died in the crash, unlocked the feather mechanism at Mach 1.0 instead of Mach 1.4. The unlocking of the mechanism in the heavier air during powered acceleration caused the twin tail booms to deploy in conditions they were not designed to perform in. The tail booms ripped off the ship in two seconds, causing SpaceShipTwo to disintegrate.
Hart indicated that he was mistaken in his statement on Sunday night, and that officials were not sure who the pilot in the right-hand seat was who unlocked the feather mechanism. He ended the briefing without clarifying how such a mistake could have been made. Pilots are always in the left-hand seats while co-pilots sit in the right-hand one.
After the briefing, one of Hart’s deputies clarified his statement. The deputy said the co-pilot was in the right-hand seat, the co-pilot unlocked the feather, and the co-pilot did not survive the accident. That would be Alsbury, as Hart had indicated on Sunday. Peter Siebold, who survived the crash with injuries, was in the left-hand seat.
So, what’s going on here? That’s where things got really interesting.
The Washington Post has a story on its website tonight that likely explains what Hart was trying to say. Under flight rules, the decision to unlock the feather mechanism is not the co-pilot’s alone but involves communication with the pilot — in this case, Siebold. I’ve added emphasis to the relevant text.
Employees at Scaled Composites, the firm that designed the space plane, on Friday were able to watch video camera feeds from inside the cockpit and outside the spaceship during its flight.
“There are dozens of reasons why mistakes like this one could be made,” said another Scaled test pilot.
That pilot went on to explain that there was a rule that anyone flying the spaceship could not re-configure the vehicle without the verbal acknowledgment of both pilot and co-pilot. It is unclear whether that protocol was followed. Normally, the co-pilot would announce when Mach 1.4 had been reached — the proper speed to unlock the feather. The pilot would acknowledge and command the co-pilot to unlock the feather. Once the feather was unlocked, the co-pilot would announce the maneuver had been completed.
A number of sources, who spoke on the condition of anonymity because the company has forbidden interviews with the media, described seeing Alsbury unlock the feather and then appear to realize there was an error, moving quickly as if he was trying to shut off the motor, but it was too late.
These sources said that within the company, there is a growing recognition that Alsbury, the co-pilot, unlocked the feather early, although it is not clear why. Colleagues say Alsbury was one of the sharpest test pilots on the team, with more than 1,600 hours of flight experience in more than nine different aircraft.
The first 15 seconds of the burn are incredibly chaotic for the pilot and co-pilot. Lighting the rocket motor is akin to opening the gate at a rodeo — the bull starts bucking and the pilot is just along for the ride, tossed back into the seat with three times the force of gravity and pushed down with even more force.
During this period, the pilot and co-pilot go through their flight-test cards, performing a number of “housekeeping” duties meant to prepare the ship for the remainder of the flight.
I asked Hart whether investigators had been able to review cockpit data to determine what the pilots were seeing on their instruments in terms of air speed. He said that they had not yet reviewed that data.
Hart said that the investigation team would be forming a new human factors group that will investigate human-machine interactions and their possible impact on the accident.
23 responses to “SpaceShipTwo: Were Proper Communications Protocols Followed on Feather Unlock?”
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When you say motor, do you mean feathering motor, or rocket engine?
From the PF02 video it’s clear that the pilots don’t follow a set-piece dialogue (verbal acknowledgement). The pilot says “5 seconds to go” and the co-pilot says “unlocking” immediately after.
Edit: changed to PF02.
https://www.youtube.com/wat…
It’s PF02, but you have a valid observation. The feathers are being unlocked during PF well before 1.4 mach.
Thanks for the correction. Also note SS2 is under considerable load (listen to the pilots breathing), yet the feather doesn’t move until commanded. I would be very surprised if it could moved purely from transonic flow.
Agreed, I have watched this vid many times. It just doesn’t jibe with what appears to have happened on the accident flight. Accidents are usually a combination of events or conditions, so I am not convinced that unlocking the feathers was the only cause. Stay tuned!!
I read someone speculate that the deploy lever already was pulled (accidentally) when the feather was unlocked. Another scenario is faulty wiring leaving the deploy lever ‘always on’. Anyway, like you I’m convinced it’s more than the co-pilot unlocking the feather a few seconds too early. If that’s really all it took to destroy the aircraft it wasn’t ready for passenger flight.
Yep, I think with all of the recording devices, telemetry and non-volatile memory, they (at the investigative level) have a good idea what happened and when it happened along with what conditions existed at the time. it’s just a matter of formalizing it for public distribution.
I agree,
I would assume that the feather “unlock” is more of an “arming” mechanism. But not know anything about the configuration or controls of SSII I am speculating.
“Pilots are always in the left-hand seats while co-pilots sit in the right-hand one.”
The distinction regarding “Pilots” in either of the Left or Right seats is (PIC) Pilot in Command.
The PIC is normally in the Left Hand seat.
Except in helicopters 😉
Which are flying abominations… so we try to just forget those exist. 🙂
Old aviation quotes:
A helicopter is a collection of rotating parts going round and round and reciprocating parts going up and down – all of them trying to become random in motion.
Helicopters can’t really fly – they’re just so ugly that the earth immediately repels them.
Helicopters don’t fly. They beat the air into submission.
Flying helicopters is like masturbation, you enjoy it while it’s happening but you’re kind of embarrassed when your done.
Helicopters don’t fly, they just vibrate against the earth and the earth rejects them into the air.
Helicopters are for people who want to fly but don’t want to go anywhere.
I’m a fixed wing guy (both powered and gliders). But I would begrudingly learn to fly rotary wing if it meant I could fly one of the tilt rotors out there. That would be a sweet job.
I am writing an interesting book which says the same thing.The black things with or without the p word are the worst.Hughes MD500s.
In this case both were rated and Siebold was PIC.
“I asked Hart whether investigators had been able to review cockpit data to determine what the pilots were seeing on their instruments in terms of air speed. He said that they had not yet reviewed that data.”
Thanks for asking a good question. It was so frustrating watching the previous conference when the reporters kept asking which lever did what.
I haven’t chimed in on the accident yet, so I want to start with offering my sincerest condolences to everyone affected by this accident, especially to the family and friends of Mike Alsbury.
The thing I have been asking myself since the premature unlocking and (un-commanded) deployment of the feathering system have been made public is: why is that system being unlocked while SpaceShipTwo is still in the powered phase of its flight anyway? Does anyone know the reason behind this approach?
The most logical answer I’ve read is that you want to ensure the feathering mechanism is going to unlock before you actually need it. If it failed to unlock, they could terminate the burn and recover the aircraft. If they waited until after the burn was over, they’d be going so high and fast that they’d likely lose the aircraft if the feather failed. Without feathering, I don’t know if the attitude control thrusters would have enough power to keep the plane in a high-drag attitude. Without that, it would pick up too much speed on reentry and likely come apart at some point.
Hmm, I haven’t thought about it this way, makes sense (kind of).
However, just because the unlocking works doesn’t mean actual deployment will work as well so you still won’t find that out until after the burn is finished.
I think I finally get how it’s supposed to work, thanks to larrj8’s explanation, and others I’ve seen at NASASpaceflight that suggest the aircraft has a tendency to feather when the tail is unlocked.
Think about it like this: SS2 is coming down from apogee with feathers unlocked, but the deploy mechanism has failed. Assuming it’s coming down belly first (which could be accomplished with RCS if necessary, assuming that hasn’t failed), aerodynamic forces will tend to push the feather up, and then once it’s up that shuttlecock configuration will want to stay that way, at least until they get to thicker atmosphere.
That makes me wonder how they would get the feather back down, and/or how landing might work with a partially or fully deployed feather that can’t be locked. Interesting questions, I’m sure we’ll learn more about it in the months to come.
i think it must have to do (at least in part) with the problem of control through the transition to the supersonic regime. i really don’t know, though i’m sure we’ll all find out a lot more about the controls and what they do and why as the investigation progresses.
I would assume that the feather “unlock” is more of an “arming” mechanism. But not know anything about the configuration or controls of SSII I am speculating.
This is the best article I’ve seen yet – and good comments too. Same as “Aerospike” I’ve been wondering about why the “unlock” during the powered flight phase. Someone who works on my plane and knows a lot about SS2 told me that the difference between mach 1.02 and 1.4 is only about 10 seconds, so somehow the assessment was made at some point that it’s safe to unlock at mach 1.4 and some (I assume) still fairly high Q (aerodynamic forces). I wonder if the unlock and feathering both happened at that point – mach 1.4 and 70-80K feet – if it would be safe or not…they are only up a few thousand feet higher in the flight profile at mach 1.4, so I assume they would not want it deploying at that time, either. And regarding the flight past the Karman line and re-entry without feather…I would think they would have a test card for that in the program at some point, unless they think the RCS jets could not keep it in a viable reentry attitude without the feathering.