Monday, November 3, 2014

NTSB: Pilot Unlocked Feathers Early

Click the arrow to watch the November 2, 2014 update. Video source: NTSBgov YouTube channel.

Ever since the SpaceShipTwo VSS Enterprise broke up over the Mojave desert Friday, self-declared experts on Twitter and space advocacy sites have bashed Virgin Galactic and its founder Richard Branson for what they claimed was a fundamentally unsafe motor design they believed caused the accident.

Now that the real experts are on the scene, those sitting in their armchairs are being proven wrong.

At a media briefing late yesterday, NTSB acting chariman Christopher Hart said that the vehicle's engines and tanks have been found intact.

NTSB investigators did find evidence that one of the pilots unlocked the vehicle's feather wings prematurely.

An artist's concept shows that SpaceShipTwo "feathers after rocket burn." Click the image to view at full size. Image source: Virgin Galactic.

According to Aviation Week:

The NTSB-led investigation team probing the cause of the Oct. 31 crash of Virgin Galactic's SpaceShipTwo says two seconds before beginning to break-up in midair, the vehicle's two moveable tail booms unexpectedly began to deploy into a “feathering” position.

Revealing the findings, NTSB chairman Christopher Hart says camera footage and telemetry show that around nine seconds after ignition of the hybrid rocket the mechanism that controls the stowage of the moving tails moved from 'lock' to 'unlock.' Hart adds that as the vehicle accelerated through about Mach 1, the co-pilot was seen to move the locking handle. Normal procedure is to unlock the feathers after Mach 1.4 so that aerodynamic forces do not prematurely extend the mechanism.

In normal operations the feathering device is designed to be activated outside of the sensible atmosphere before the vehicle begins its descent. In addition to the locking mechanism, the feathering device requires the activation of a second handle. The feather system acts like a shuttlecock and was originally conceived by Scaled Composite designer Burt Rutan as a carefree re-entry method for recovery of SpaceShipOne. The feathering system was deliberately deployed supersonically as a part of earlier powered flight tests of SS2. However in each previous deployment, activation either occurred in thinner air at higher altitudes, or during unpowered flights at much slower speeds than the ill-fated flight on Oct 31.

Hart stressed that the finding is “a statement of fact rather than a statement of cause.” There is no evidence yet that a pilot activated the second handle.

CNN reported:

During feathering, two pieces on the back of the vehicle — the “feathers” — lift up perpendicular to the spaceship, making the vehicle look like it's arching its back as it descends.

But on Friday, “the feather lock-unlock lever was moved by the co-pilot from the locked position to the unlocked position” prematurely, the National Transportation Safety Board said Sunday night.

On top of that, the feathers aren't supposed to move until a separate feathering handle is activated. No one adjusted that handle; yet the feathers were still deployed, NTSB acting chairman Christopher Hart said.

But Hart stressed it was unclear whether pilot error, mechanical problems or a host of other possibilities caused the spacecraft to break apart in the air.

These latest findings are a reminder that the investigative process should always be respected. The uninformed should not jump to conclusions based on media or other amateur punditry.

UPDATE November 3, 2014 10:00 AM EST — Here is raw video from a tail camera of the SpaceShipTwo powered test flight on September 5, 2013. The word “unlocking” is spoken at the 37-second mark in the footage.

Click the arrow to watch the film. Video source: VideoFromSpace YouTube channel.

1 comment:

  1. If you look at previous flights, feather mechanism unlocking occurs about 10 seconds after engine start.

    It is too early to say it was not the engine that caused this disaster, we only know there was no explosion.