FlightAware Discussions

NTSB report Bedford MA GIV crash


#1

The NTSB report seems to say that the pilots rushed the takeoff and did not remember that the gust lock was ON thus disabling the elevators. They blame manufacturer for a throttle interlock system that was so ineffective that it allowed the pilots to advance the throttle to 22-26 degrees and thereby reach 187 mph. The wreckage reveals the gust lock lever in the OFF position. I am not a pilot and have never been near a Gulfstream. Here are my questions.

  1. How unlikely would it have been for two professional pilots to forget to disengage the gust lock lever.
  2. Could the plane have reached that “V1” and “rotation” speed with the throttle limited to 26 degrees.
  3. Could the elevators still have been locked with the gust control lock OFF.
  4. Would a pilot routinely test the elevators before reaching V1.
  5. How impossible would it have been for someone not on the flight to have tampered with the system.

#2

This squawk was posted this week regarding the subject:
flightaware.com/squawks/link/1/7 … er_s_Owner


#3

The control lock is normally disengaged during the before start checklist. See 3 above.
The above answers assume the system is the same as the G2/3. It looks like it is similar, the 2/3 does not have an intermediate setting, I am assuming that with the lock handle partly stowed the throttle could be unlocked but the controls still locked. That would likely require a broken system. It is a system made up largely of cables and pulleys.


#4

Thank you to the experts. Here are my concerns. The report says the pilots tried frantically and unsuccessfully to release the gust lock as the jet proceeded on the take-off roll. Why couldn’t they release it? Doesn’t it seem like they were surprised that the “lock was on” because the handle apparently showed it to be OFF. Why would there be an intermediate position for the handle? That makes no sense.


#5

On the ground the elevator rests in the nose down position thanks to gravity. That is also a good place to lock it. Roaring down the runway there is a mighty air load trying to move the elevator towards a neutral position. Being nothing more than a cable and pulley system with a locking pin the forces required to disengage the pin would be pretty serious. Try unlocking a deadbolt on your front door with somebody leaning on the door causing the bolt and slot to not quite line up. This would be 100 times worse.
There is no intermediate position but sometimes the lock has trouble releasing for that same reason, in my experience when there is a strong tailwind trying to push the rudder sideways. As far as I know there are pins on all three controls, one elevator, one rudder and one of the ailerons, any of these could be jammed not letting the control lock handle move to the full off position.


#6

The plane rolled away from the terminal at 9:33. **b]The pilots apparently never tested the elevators by pulling back on the yoke during the following six minutes of taxiing that preceded their final 50-second takeoff roll.
**
The plane made two left turns and at least two right turns as the plane taxied toward takeoff. These turns may be significant.

As the jet turned onto the runway, the pilots noted that a blue warning light — the “rudder limit light” — had gone on. This baffled them.

“Are you using the rudders?” McDowell asked De Vries. “No.” “Huh.”

Here the pilots made a new error. Rather than stop to figure out what had triggered the warning light, they kept going with the takeoff.

Following postcrash testing, including re-creations of accident scenarios with test aircraft and flight simulators, investigators learned that the rudder limit light was far from a model of clarity.

The light glows blue if pilots keep stepping on the rudder pedal, pushing the rudder to its limit.

But it can also illuminate under certain conditions when pilots turn the taxiing plane to the right. And, investigators found, it can illuminate when the elevators are locked

This passage is from the Inquirer article. It says in 6 minutes of taxiing the pilots never tested the elevators. Is this conceivably likely or is it more likely that they thought the elevators were OK. I assume they can not be seen from the cockpit.


#7

That reminds me that the rudder limit light check typically is done as part of the “controls free” line on the after start checklist. The rudder limit system reduces the hydraulic pressure to the rudder to keep the pilot from twisting the tail off the airplane during a low speed-single engine event. They think that is what caused the American A300 crash near JFK after 9/11. On the Gulfstream there are two lights, one red that indicates no pressure to the rudder limiter and the blue light. The red light normally goes out during engine start, the blue comes on as you near full deflection during the control check.
Correct, the rudder and elevators cannot be seen but the G 4 and later models have a cute drawing on the eicas display that shows actual control surface positions.
The accident report seems to focus on the elevators. The gust lock freezes all of the controls so had there been much of a crosswind or an engine failure they would have been in trouble much earlier.


#8

OK “the gust lock locks all of the controls” so for this accident to have happened the way it is being explained the pilots —there were two in the cockpit — would have to have operated the jet on the ground for six minutes with all the controls disabled and the throttle advance limited to either 6 or 22 degrees without suspecting anything was wrong. Is this a credible explanation.


#9

sort of. To be technical the controls are not disabled but are locked and they would have had minimal throttle movement available. That is all assuming the gust lock was not broken, it is nothing but cables and pulleys, and locked just the elevator with everything else available. With the severity of the wreakage that is something we may never know for sure. Except for the control checks that have been previously discussed there is no big reason to move the controls before takeoff.


#10

Thank you. Final question is about the throttle. The report is going to slam the manufacturer. Saying the 6 degree limit actually manifests as a 22 degree limit on throttle advance. Again, is it reasonable to state that the pilots did not detect the 22 degree throttle lock before reaching V1. How about omitting the checklist in a corporate setting. Would that be common.


#11

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#12

No, corporate pilots are taught to use the checklist. Every operation I have worked for use it.

As I remember the system, it’s been a couple of years, it is designed to let maintenance personel start the engines and run both at idle or slightly above idle…6 degrees. If they need more power on one engine that throttle can be advanced to as much as 22 degrees but the other throttle is physically moved back towards idle at the same time. If a full power engine run is needed the gust lock must be disengaged.
It seems obvious that some part of that aircrafts gust lock system was broken.


#13

More on this accident:

The NTSB report

ntsb.gov/investigations/Acci … AR1503.pdf

Blames the pilots, mostly. No preflight checklists performed for the flight. In fact, they hadn’t done any checklists for roughly the last 175 departures. Hmmmmm…

An analysis by Ron Rapp that…uhhh…blames the pilots, not the gust lock.

rapp.org/archives/2015/12/no … -deviance/

Rapp sends the reader to Code7700, who…wait for it…blames the pilots, and goes much further.

code7700.com/case_study_bedford.html

“That gust lock, however, is a red herring. (An irrelevant topic introduced to divert attention from the important issue.) Yes, a better design of that gust lock could have prevented the mishap but consider the following. The GIV gust lock system is identical to that installed in the GII and GIII before it, almost identical to the GV, G550, and G450 that followed. And yet this is the first mishap of this type. That gust lock has been around for over a half century.”