If you look at the photo in post #35 the nose gear was torn off when the aircraft left the runway and the tires are still intact.

Also noticeable is that anti-skid was operational.

three three mike

thanks

I guess what I am saying is maybe the plane thought it was in the air and the anti skid didn't work, and then the plane thought it was on the ground and then it did start working.

if the tires are intact, we can assume they were not sucked into engine. but maybe something else like owls were.

Yes, there is a control lock - it is a red lever on the center console that is engaged by pulling it up to a latched position. It will lock the ailerons, elevators and rudder.

While the lock is fine for preventing the control surfaces from moving in gusty winds, it is not all THAT durable. The locking mechanisms could be easily overpowered (which is to say broken) by the power available to the control surface actuators once hydraulics come online.

For that reason, releasing the control lock is called out in the BEFORE starting engines checklist, as breaking the locks is a definite possibility once hydraulic pressure builds up, if an attempt is made to to move to move the yoke.

There is also a checklist requirement to test the stall barrier (stall warning) system before flight, after engine start. This entails pulling the yoke full aft, while the PIC and SIC, simultaneously press test switches, (each on their own side of the cockpit) for several seconds. This tests the AOA sensors, the stick shaker, and (lastly) the hydraulic stick pusher. Again, it would be impossible to perform this op test with the control lock engaged.

The ailerons and elevators are mechanically controlled via standard cables, pulleys, sectors etc. Ordinarily, the cables also control the hydraulic boost actuators at the control surfaces, but even in the case of a dual hydraulic failure, the controls would go to full mechanical reversion, meaning the surfaces can still be moved solely by pilot "muscle power" - Although it would be like manhandling a Mack truck without power steering, it would not be like losing all hydraulics in a purely FBW aircraft.

The GIV is not particularly "touchy" about elevator trim either. Some aircraft require the trim to be set to within a degree (or less) of a pre calculated value before takeoff, based on current CG. On the GIV, setting the trim to "somewhere in the general vicinity" of 10 degrees is usually perfectly fine. Which is to say that the "green band" on the trim wheel is quite wide.

Horizontal Stabilizer trim is a different matter though. The entire H-Stab moves progressively leading-edge down, automatically as the flaps are deployed. On the GIV this is accomplished by a rotating torque tube, running up the inside of the vertical stab, that is driven by the same hydraulic motor that drives the flap jack screws.

On later-model Gulfstreams, the H-Stab is driven by its own actuator, which is independent of the flap drive actuator.

Not being a GIV pilot, I am not sure what effect on pitch authority would result, if for some reason, the Horzontal Stab did not move to the proper position for the selected flap setting. I can think of several ways such a failure could occur from a mechanical perspective. The flap position indicator on the flight deck is a dual gauge, which shows both flap and H-Stab position, but am not 100 percent sure if an H-Stab not set properly would generate any other config warning (I.e. CAS message etc.) on the GIV. I'll have to check my maintenance manuals tomorrow.

JRB

thanks for your expertise.

I just want to understand for sure that this type has both ELEVATOR trim (tabs) and moving stabilizer? interesting.

I understand about the movement to counter flap pitch change. just interesting!

Correct. The horizontal stab physically moves as the flaps extend to counteract the change in pitch induced by the flaps - and the two (flaps and hstab) are mechanically interlinked. The horizontal stab basically has 4 fixed positions for flaps up, flaps 10, flaps 20 and flaps 39. (though it does move continuously between these fixed positions as the flaps run in or out).

Once the flaps are fully retracted, the H-Stab moves back to its "normal" position, and remains fixed there, with normal trim authority coming exclusively from the elevator trim tabs.

This is different than other T-Tail biz jets, eg: the Beech 400A, where a moving H-Stab (electrically actuated) is the primary source of manual and autopilot trim - likewise for most Lears.

A few years ago, I spent a couple of months riding in the jumpseat of a GIV, being operated in Africa. Due to the lack of mx services at many of the airports, the aicraft owner wanted a mechanic onboard for all trips.

The only time I ever saw flaps 10 used for takeoff (as opposed to 20) was the very scenario you describe. Departing heavy from Abuja, Nigeria, on a day that was close to 40C. The crew had a long preflight discussion about second segment climb performance - most of which went over my head - but the decision to do a flaps 10 departure was determined to be the only safe option. I do recall that ground roll and v-speeds were quite a bit higher than what I was used to seeing.

Still, I'm no expert as to the operational/piloting aspects of the GIV, other than knowing that it would be difficult to accidentally takeoff with flaps 10 (when 20 was intended) due to the conflict between actual flap position and FMS takeoff init, which would prevent v-speeds from displaying if the two did not correspond.

Hard to say about the thrust reversers based on the photo. Both T/R and ground spoiler deployment require positive weight-on-wheels, but as I mentioned in another post, the T/R "buckets" are held open solely by hydraulic pressure via their actuators - there is no locking mechanism to hold them open. If hydraulics were instantaneously lost due to the ongoing disintegration of the fuselage as the overrun progressed, combined with rapid deceleration of the airframe, I can envision a scenario when the T/R doors POSSIBLY could have been thrown forward and (mostly or completely) closed from inertia.

One of the news reports on Sunday, quoted a woman who lived near the airport who said that the engines were "really screaming" just before the sound of the crash and breakup. Cound have been a last ditch attempt to firewall the engines to get airborne, but based on the skid marks, equally likely to have been the sound of an attempt to apply max reverse thrust.

Hopefully the FDR and CVR will shed some light.

Glitchy,

Once it becomes public knowledge, it is in my opinion OK to post the names...

More thought provoking is the photo above your post, showing the skid marks and overrun....

Many of us have or almost have been there, but knowint this view was one of the last views that flight crew would ever see is definitely eerie....:sad:

It looks like they tried to go after they left the runway.

The runway skid marks show that the tyres were intact and braking when they left the runway so its not a main gear tyre failure.

But there is no other obvious drag device deployment - the TRs look like they are still stowed and the Ground Spoilers dont look deployed.

The main gear furrows after the runway end stop almost coincidentally with the loss of the nose gear as if the braking stopped (lost the hydraulics?).
After that point (with no brakes) there are obvious brown singe marks from both engines (both producing thrust) on the grass from high thrust at a high nose angle just before it hit the approach light berm.
Fire then started from that point.

In an abort in the GIV, if the throttles arent pulled to a point very close to the idle stops then Ground Spoilers arent available and Reverse Thrust requires the throttles to be at the idle stops. If they arent back then residual forward thrust will not be helping the attempt to stop either.

What a terrible little gulley to have just off the end of the runway - a survivable and slow impact here probably caused the breakup and fire.

Were the crew experienced GIV guys?

here is a diagram of the runway. note the over runs on both ends.

http://155.178.201.160/d-tpp/1406/00626AD.PDF


a thought struck me that perhaps the pilots took off from an intersection by mistake and didn't have sufficient runway for takeoff.

just a thought mind you.

doesn't it remind you a bit of the lexington, kentucky crash of the RJ, taking off on the wrong runway

Door/Boarding Stairs Deployed
 

From the photos, it looks like the boarding stairs were deployed. I wonder it there was an evacuation attempt or did rescue personnel open the door?

Some tragic pics:

Wreckage of private jet that killed Lewis Katz and 6 others revealed | Mail Online

A fairly comprehensive set of photographs

Photos: Crash at Hanscom (Photo 1 of 31) - Pictures - The Boston Globe

Jfill,

Judging from all the smoke and soot on the stairway of the air stair I would say that it was likely opened in an evacuation attempt. It is also possible that the impact with berm caused the door to come open like that.

Another thought I had is that perhaps the door came unlatched during the take-off roll and it was the "Door Unsafe" CAS message that triggered the abort.

It's impossible to tell from the photos whether or not the Ground Spoilers deployed, but as Mr Barrett points out if they were not not armed, the crew would not be able to get their speeds to "box" along with a blue CAS "Ground Spoiler Unarmed" CAS msg when they took the runway. It is permissible to dispatch any Gulfstream with the Ground Spoilers disabled, however it requires the use of Flaps 20 and Anti Skid functioning on a non-contaminated runway to do so. In this case the Flaps were supposedly set at 10, so that would seem to remove that possibility.

About the only thing I can deduce from the accident photos is that the elevator Trim appears to be correctly set nose up and the Thrust Reversers were not deployed, which makes me wonder if the crew pulled on the piggyback levers to command them but for some reason the buckets failed to deploy and they got forward thrust instead. I recall a Lear accident a few years ago where a tire blew on the take-off roll and pieces of the tire disabled the W.O.W. System preventing deployment of the T/R's, the aircraft subsequently went off the end of the runway at considerable speed because they thought they were commanding reverse thrust when in fact they were getting forward thrust.

Little more info - CVR and FDR recorded everything.

Doesn't confirm where on the runway the run started but is sounds like threshold.

Normal takeoff - call out 80 knots, V1, Rotate, aircraft did not rotate - not being specific what
was said, but pilots confirmed loss of control - speed at 165 knots.

Thrust reversers deployed, heavy braking - 7 seconds later - last recorded speed 100 knots

from start of take off to end of cvr tape 49 seconds.

No wildlife reported.

astra

yes, I mentioned that lear/ wow thing earlier.


how wouldyou like to get to V1R and pull back and NOTHING HAPPENS?

amazing synopsis of the cvr. thanks robbreid.

sounds like flight controls are suspect, or at least W&B questions. Remember that Challenger that had a forward C/G and couldn't rotate ? everyone survived that one.

Just curious, but how do you have this information ?

A word of caution is in order:

Much has been said here. Most of the systems information and references are correct, a few are a little off, but substantially correct.

However, the conjecture being put forth is premature, and I would hope that people posting would make sure that they are posing a question, not putting forth fact...

This latest news article talks about the 49 second recording

UPDATED: Flight records capture the 49 secs of the plane's movement - News - Lexington Minuteman - Lexington, MA

From an email I received from Aviation International News (public release)

jrrbarret

i can imagine that if the stab trim did not command nose up<with flap position> ( leading edge down) that it would be difficult to rotate. wondering if it has ever failed?