B-2 crash accident report, deux

Military aircraft accidents/mishaps.
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by Gums » 06 Jun 2008, 19:48

Salute all!

I place this up again, as the other thread is too long and it does not "cut to the chase".

The URL has access to sections of the actual accident report and does not have a lot of PR stuff from media.

http://www.alert5.com/2008/06/b-2-accid ... eased.html

I also think this is a better thread to discuss differences between the Viper and the Spirit FLCS than the other thread that has been edited/censored.

Gums sends .......
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by Hookturn » 08 Jun 2008, 00:39

The accident report findings for sure will ripple a long way.

Any idea on how many heads will drop? I bet the drivers themselves are on a clear water?

late edit: I probably would have castrated the guys for being so long with the plane...


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by johnwill » 08 Jun 2008, 02:46

Gums,
Thanks for the link. Very interesting read. First impression - Northrop got trapped into the Airbus style of giving the FLCS too much authority to override pilot commands. AoA reads too low, so apply max nose up command? Absolutely insane. Nz ok, positive rate of climb, altitude ok, pitch rate ok. All match pilot command.

The obvious cause of the accident is stupid flight control engineering. Sound like Viper FLCS power supply stupidity? Does to me.

If AoA went bad, why didn't the FLCS just switch to standby gains and turn on the master caution?

I'm no flight control expert, but I can smell a screwup here.


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by Gums » 08 Jun 2008, 03:07

Horrido!

TNX, John-boy.

You may not have been here long enuf, but we had a real Viper driver who's log-in was "STBYGAINS".

What bothers me as much as no reversion to STBYGAINS, is the display of IAS and altitude using the same porked sensors that screwed up the FLCS.

Can't help but wonder that if the guys would have rotated 15 knots faster using the pitot-static system they might have given the FLCS time to settle down.

I also wonder how much bodyrate input that thing uses. Hell, it's a huge plane, and if it feels like a 747, who cares? Some bodyrate input would have helped a lot. Also note the 1.6 gee initial climb due to the FLCS, not the pilot input. Seems to favor the Viper gee-command blended with AoA and bodyrate inputs with gear down.

When I helped Northrop and the lawyers back in 1985, GD was the AntiChrist, I tellya. 'course, GD had underbid the hell outta some Vipers for Korea, so I had some sympathy for the F-20 there. It would not surprise me that they didn't want a single idea from the GD FLCS control laws.

We need to get Roscoe in here or maybe a Raptor jock.

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by asiatrails » 08 Jun 2008, 18:15

Gums, thanks for the direct pointer, the rest of the verbage gets in the way.

This is a human factors issue and reminds most of all of the Aero Peru 757 crash where it was washed with the pitot sensor ports taped over but they did not remove the tape before the aircraft took off with a full load of passengers and crashed.

A good summary of human factors can be found in Appendix 4 of the Space Shuttle return to flight report. The appendix starts on page 88.

http://history.nasa.gov/siat.pdf


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by huggy » 08 Jun 2008, 19:35

Hookturn wrote:I bet the drivers themselves are on a clear water?

late edit: I probably would have castrated the guys for being so long with the plane...


:shock: Did you read the report?


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by brancwp » 10 Jun 2008, 21:20

Here is the official report and video of the actual crash.
http://www.acc.af.mil/accspecialreports ... nboard.asp
As one of those that helped design the Flight Control System, I have to say it is one of the most crash proof aircraft in history!
The cause was an Air data calibration done while there was a bias on the overhead GLA sensors (due to moisture..but I would have to say we are talking lots of water here!).

Yes an Air data calibration can cause loss of aircraft - much like an inproper rig of the control surfaces.
The B-2 has 28 flush ports going into 24 computers (PTUs), there is lots of cross comparisons and checks done with the Inertial data also. And yes we have back-up fail-safe control system mode for Air Data Failed. It is interesting to note the FCS did flag a caution for the air data system while on the takeoff roll. It should have happened at 60 knots (the reports says it was indicating over 100 knots - but I have to doubt that since they talked about it and had time to check the page before it reset). It did flag the entire Air Data system failed at liftoff and revert to back-up gains. The pilot can overpower the system (AOA is just a feedback and a limiter like many other inputs), but the low airspeed and quick pitch response caused a stall. Maybe the aircraft could have been flyable but the pilot would have had to point the nose to the ground to pick up speed and then pull up slowly just before the ground - not instinctive. Yes another 10 knots of airspeed and I am pretty sure he would have recovered it. The pilots to blame? Only because they could have aborted on the takeoff roll when the FCS CAUTION happened - Guam is not exactly a short runway - damn the "we use 100 knot abort guideline". What happen to calculating the abort speed? It would have been well above the speed they were at. Maybe some blame for not recognizing the difference between the runway altitude and pressure altitude. People blame the Kentuky pilots for not noticing the difference between the runway heading and takeoff heading in a commuter lane crash.

Maybe some blame on maintenance for not insisting on understanding why these things need Calibration so often. Maybe some on procedures not requiring heater on during cal to remove water. Maybe some on procedures which do not require a baro setting check against actual HP channel by channel after the cal. Maybe some oon procedures which to not require a dynamic pressure test set to cal across the range of pressures.

Maybe some on the designers for making it too dang easy to just push a button to recal these things anytime someone in the cockpit wants to.

But for the record I for one will take a lessons learned to try and design the next system better. Unfortunately there are still zero fuel mass properties files, air data calibrations, Surface rigs, weapons loadings, and IMU installation correction data, hardware compatibility issues, etc that all rely on "procedures" to mitigate the risk of LOA.
Last edited by brancwp on 11 Jun 2008, 18:05, edited 3 times in total.


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by Gums » 11 Jun 2008, 00:25

Salute!

A big thanks, Bran. this helps.

Your comment about "refusal speed" is right on the mark. For those of us that rolled 85% of the available runway carrying 10 x 500 pounders, we had two check speeds plus the refusal speed. think SLUF at Korat in 1972.

My problem with the crew is not starting over when they got a FLCS warning light on the roll and didn't stop and start over.

My second problem is using the same air data for the "steam gauges" or the cosmic display panel equivalent.

I am also disappointed that it only took a handful of mis-calibrated air sensors to cause the 1.6 gee pull and 25-30 degree climb.

As you said, I think a few knots more before rotating and the crew and FLCS might have enabled a recovery - scary, but maybe make it.

I am sensitive to the LO principles that require all those flush-mouinted sensors. So unlike the Viper, the Spirit has to use other methods than the pitot tube.

Crying shame, but I commend the crew for staying so long and doing all they could except aborting at 50-60 knots when they got the FLCS warning light.

Gums sends ....
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by Elliboom » 11 Jun 2008, 12:40

I will defend the 100 knot abort statement. We also have the same abort guideline, but we will tend to take anything that happens after 90 knots into the air. True your real refusal speed is alot higher, but anything over 90-100 knots especially when you are talking high gross weights like they most likely would have had since they were redeploying home and you are talking a high gross weight, high speed abort. History has shown especially lately that high speed high weight aborts tend to lead to more accidents, damage and injuries then just taking a heavy jet into the air. Now this is obviously contrary to what you would do in a single engine fighter, but when you are talking a jet with 4 engines, you tend to have a lot of options once you get into the air.
For years the Air Force trained that refusal was a black and white type of thing in the heavy jets. If you were below your refusal speed you aborted, if you were above you took it in the air. But the number of abort accidents has skyrocketed since the early 90's when we started flying in desert climates on a daily basis, and that is simply becasue you had alot of guys aborting for simple problems at speeds approaching refusal. And while they may have gotten the airplane stopped, they had to stand on the binders to do it, thus locking up tires, blowing tires, shredding flaps, causing gear fires, and generally f'ing up a ton of iron. So now the air force is treating refusal more like the airlines do, and that is to establish a set speed usually around 90-100 knots when you will take almost anything into the air. Obviously these guys did not feel that their problem was serious enough to warrant a high speed abort, which also most likely would have resulted in a class A on the aircraft anyway. It may have been repairable, but it would probably ahve been a mess.
Luckily they got out of the jet, and will live to fly another day. Hopefully this accident will be a lesson, and some changes can be made to prevent another accident like this from happening to the B-2 or any other aircraft with a similar type of control architecture.


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by Hookturn » 13 Jun 2008, 23:48

brancwp wrote: Only because they could have aborted on the takeoff roll when the FCS CAUTION happened - Guam is not exactly a short runway - damn the "we use 100 knot abort guideline".


Thank you for this.

My initial inquiry was sparked because I feared that some of those with too much blingbling on their collars would think that we should be robots and _instantly_ figure out what's happening thus finding a way to ground the crew as well.

And I blame the beer as well. Sorry about that.


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by Asif » 14 Aug 2008, 21:54

Stars & Stripes wrote:B-2 mission commander recounts February crash on Guam runway ‘We gotta get out’
By Charlie Reed, Stars and Stripes
Mideast edition, Friday, August 15, 2008


Capt. Justin Grieve knew something was wrong as soon as the B-2 Spirit left the ground.

Within seconds, water in the sensors caused the $1.2 billion bomber to spiral out of the control of Grieve, who was flying in the mission command seat, and pilot Maj. Ryan Link. They were on their way back to the 509th Bomb Wing, home of the B-2 bomber at Whiteman Air Force Base, Mo.

"As soon as the plane did something that I knew [Link] wasn’t doing, I said, ‘We gotta get out,’ " Grieve recalled Wednesday during his first interview following the Feb. 23 crash at Andersen Air Force Base, Guam.

The plane was 30 feet off the ground when the left wing struck the runway and Grieve made the fateful move to eject — a function that works simultaneously for both pilots during take-off.

"We didn’t have control of anything. We were along for the ride," he said. "It felt like the plane was going to crash. I remember looking at my hands and saying ‘You’ve got to be kidding me.’ I put my head back, closed my eyes and pulled as hard as I could."

After rocketing 100 feet into the air, Grieve hit the ground with a thud. The bomber exploded just 50 yards from where he landed — the most costly loss of an Air Force aircraft in history.

It was a move Grieve, 30, believes he made thanks to his background as a flight instructor.

Because of the B-2’s cutting-edge technology and flawless safety record before the incident, another set of pilots might have perished trying to regain control of the costly jet.

But Grieve, of Bedford, Texas, followed the steps he had doled out on so many occasions to pilots in training: If the plane is going to crash, get out.

"It was a plane and it wasn’t working right," said Grieve. "I think that mentality saved our lives."

Ryan survived with only minor injuries, but Grieve broke his back and spent the better part of four months in a back brace, unable to fly or even drive.

He got back into the cockpit for the first time about six weeks ago, a little shaky but far from unnerved.

When it crashed, the "airplane was doing exactly what it was supposed to be doing," he said. "That’s the crazy thing. It was just a matter of bad data in, bad data out. … I have so much faith in the B-2 as a plane that it hasn’t thrown me off my game."

Moisture trapped in three of the 24 sensors that feed information to the bomber’s computer system made the plane think it was pointed downward, causing the nose to suddenly jerk upward and out of control, according to an Air Combat Command crash report issued in June.

The report cleared Grieve, Ryan and the maintainers responsible for the bomber of any wrongdoing.

Last month Grieve met the technician who packed his parachute, Staff Sgt. Genevieve Simmons.

"It was a teary-eyed moment for both of us," said Grieve, who gave Simmons the Air Force coin he was carrying during the crash. After their meeting, Simmons, 24, asked Grieve to act as her re-enlistment officer.

"It was really meaningful," said Simmons, 24, by phone from Whiteman Air Force Base. "It’s something that not many people in my career field ever get to experience. When a plane goes down, everybody usually dies. You don’t hear about a good ejection very often."

While Grieve, a husband and father of one, considers himself lucky, he doesn’t think of the incident as a near-death experience.

"My dad said, ‘You didn’t almost die. You did exactly what you were supposed to do.’"

source: http://www.stripes.com/article.asp?sect ... icle=56766
Asif Shamim
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