Continental 737 Off Runway at DEN
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I know there are a lot of photos, but this one is a little clearer and sharper.
http://extras.mnginteractive.com/liv...RASH_GRAPH.pdf
http://extras.mnginteractive.com/liv...RASH_GRAPH.pdf
The hypothesis would then be that there was reduced braking power on the right main gear. But I admit it sounds far-fetched. The difference between left and right track might just as well be due to drifting snow filling the right track. FDR will tell, I presume.
When it comes to the nose gear, I think those faint tracks are real enough. If there was some frost on the grass, it would not get much displaced when the nosewheel rolled over it, unless the wheel was skidding. The main gears with brakes applied are another matter and they would tear up the frost easily.
Just my 2 cents
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Originally Posted by edmundronald
3g shutdowns ...
As an electronics engineer who hasn't been active for years, I do find 3g shutdowns by design a bit strange.
It's pretty easy these days to design a device which can stand much more; in fact I'd be willing to bet that your average flash-RAM ipod packed in a few inches of polystyrene would stand a LOT more.
As an electronics engineer who hasn't been active for years, I do find 3g shutdowns by design a bit strange.
It's pretty easy these days to design a device which can stand much more; in fact I'd be willing to bet that your average flash-RAM ipod packed in a few inches of polystyrene would stand a LOT more.
So far we don't know what type of FDR was on this particular aircraft.
I would agree, that for a recent FDR with solid-state memory, a 3g limit seems faintly ridiculous.
It seems odd even for an HD type recorder.... portable PCs get that sort of "input" regularly. I admit it would probably leave a "scratch" on the record, because it takes milliseconds, not microseconds, to lift the head and park it.
As an aside, re back-up power, after a, say, 10g event, or full loss of all power, we may not want the recorders to run TOO long... they may well be damaged enough to overwrite the data we want to look at ....
CJ
While we're waiting for further from the NTSB, the recorder sub-thread is indeed interesting. Of greatest interest will be, did a "3g switch" turn off the recorders on this airplane as it was hitting the berm after the small ravine "leap"? Of secondary interest, did the same kind of puzzling arrangement shut off the Madrid MD83's recorders, an accident of which this one was very nearly a copy. The Madrid aircraft's subsquent hard landing from the initial stall would certainly have been greater than 3g's. To repeat, I know of a greater-than-3g landing and the recorders kept going. This has to be really old technology.
Re
That was the problem with SR111 of course - there is a crucial six minutes or so of flight and CVR information that was lost because all electrical power was lost as the fire progressed through the overhead panel. A separate source of power for both recorders has been in discussion since that accident. This accident may highlight such a change. We'll see.
Re
re back-up power
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PJ2,
In this particular case, a "3g cutoff" would only have impeded recording the final bumps, not the initiating events.
But from what's been said here, one does start wondering about FDRs and CVRs... is enough being done to make sure they go on recording when they should?
Let's tread very carefully here, but ... for instance.... when the power to the FDR (CVR, QAR) disappears does that mean automatically everything else is already off-line?
CJ
In this particular case, a "3g cutoff" would only have impeded recording the final bumps, not the initiating events.
But from what's been said here, one does start wondering about FDRs and CVRs... is enough being done to make sure they go on recording when they should?
Let's tread very carefully here, but ... for instance.... when the power to the FDR (CVR, QAR) disappears does that mean automatically everything else is already off-line?
CJ
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It just seems to me that many events could initiate with a > 3G load, and that the design of any recording device should be such that it would continue recording subsequent events until the aircraft reaches a stationary state, assuming that the event is not an in-flight explosion or other total destruction of the aircraft.
Shouldn't these devices be capable of recording events right up to the point of total catastrophe? They are clearly designed to survive catastrophe, but if they stop recording when things are just becoming uncomfortable, what use is that?
Shouldn't these devices be capable of recording events right up to the point of total catastrophe? They are clearly designed to survive catastrophe, but if they stop recording when things are just becoming uncomfortable, what use is that?
Last edited by thcrozier; 24th Dec 2008 at 07:22.
CJ;
Yes, understand, thanks.
Likely so in the scenario I image - the recording devices would simply keep falling back on the "next" source of power until the last source, likely battery-backup, was exhausted, say, after 10 or 15 minutes. Likely longer wouldn't be needed because an airplane at that stage of electrical capability isn't going to be in the air long. (That said, there have been some interesting A320 DC Essential Bus failures, (DFDR is powered by the AC1 bus), which have blacked-out all or partial instruments, as we know). I note for example, that the Bombardier Global Express accident report cited above, indicates that the DFDR is powered by the DC Essential Bus - that type of bus, as indicated by it's name, is "normally" a backup power source for the main DC busses for essential services only so it appears as though Bombardier has considered this scenario - I'm guessing here of course.
In this particular case, a "3g cutoff" would only have impeded recording the final bumps, not the initiating events.
when the power to the FDR (CVR, QAR) disappears does that mean automatically everything else is already off-line?
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From my experience I remember the B737 with winglets being very squirrely in strong gusty crosswinds. Applying significant or full aileron correction into the the wind seem to be the only way to keep it tracking the runway center line.
Guys that applied minimal or no aileron correction because they didn't want spoiler deployment seem to be all over the runway.
Maybe they caught the runway edge/lights?
Guys that applied minimal or no aileron correction because they didn't want spoiler deployment seem to be all over the runway.
Maybe they caught the runway edge/lights?
Sean737L1011;
Then there is either a certification or a training issue, (perhaps over-controlling the rudder). Also if one doesn't have one's feet on the floor but instead rides the toes at the top of the pedals, there is a risk in inadvertently applying brakes, although the risk is to the downwind brake being applied because it is downwind rudder being applied. Regardless, no transport should require "full aileron" into wind to keep the wing down - the roll-spoiler drag pulling the aircraft into wind can be a real issue - some worse than others. The 320 requires no aileron below 20kts if I recall the AOM advice.
From my experience I remember the B737 with winglets being very squirrely in strong gusty crosswinds. Applying significant or full aileron correction into the the wind seem to be the only way to keep it tracking the runway center line. Guys that applied minimal or no aileron correction because they didn't want spoiler deployment seem to be all over the runway.
Nose Wheel Bogey ??
Looks like something may have broke on the nose wheel bogey during TO runup.
Thumping sound heard in cockpit and TO abort called by crew.
Could these pics show the nosewheel bogey?
=============
John
Thumping sound heard in cockpit and TO abort called by crew.
Could these pics show the nosewheel bogey?
=============
John
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At the speed reported by NTSB they were near or at Vr as I have heard reported. I have dealt with imbalance, worn scisorse on nose wheel gear
that shook like hell after rotation. An AC that size should not be affected to that extent. Should not. But possible. But to take the AC off the runway? Perhaps an extream shimmy called for an abort but what then? Still too many questions.
that shook like hell after rotation. An AC that size should not be affected to that extent. Should not. But possible. But to take the AC off the runway? Perhaps an extream shimmy called for an abort but what then? Still too many questions.
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Nose wheel bogie?
flynerd,
Comparing the size of the wheels with other features of the aircraft to determine scale and assuming the picture from the right side of the aircraft was taken with a tele lenz, I guesstimate that to be a main wheel bogie.
Green-dot
Comparing the size of the wheels with other features of the aircraft to determine scale and assuming the picture from the right side of the aircraft was taken with a tele lenz, I guesstimate that to be a main wheel bogie.
Green-dot
This is an intriguing accident.
What do we know so far?
* There was an RTO initiated at >100Kts.
* They reached 119kts (IAS?) before decelerating.
* After about 2,700' of roll (2,000' go, 700' stop), they left the paved surface.
* Brakes/tyres are reported as being in working condition.
* The historical METARs show a crosswind but well within limits for a dry RWY.
* "Noises off" during the takeoff roll.
* Recordings stop at 89kts after impacting a taxiway/road/earth bank.
What don't we know:
* What the RTO was commanded for - engine failure, loss of directional control, etc.
* What happened with RTO braking, reverse, spoilers, etc.
* The flying control inputs during this time.
Speculation:
I would assume that as the aircraft started to drift to the left, corrective action would have been taken (right rudder) and that would have soon gone to full deflection if the drifting continued. This is pretty much a reflex reaction for an experienced pilot and may have happened prior to the RTO decision. From the reported weather and aircraft speed at the time, there should have been no issues with Vmcg (if an engine problem) or crosswind limits. But the 737 still veered off the runway to the left...
What could have caused this?
Asymmetric forward thrust? Unlikely, as both thrust levers would have been closed during the RTO; difficult to only close one and at the speed they were at this would lead to a SE TO. Asymmetric reverse? Possible but this shouldn't cause a problem as it's factored into the limits (normal proc. for engine fail == only 1 reverser left). Uneven braking? Again, possible but I wouldn't have thought enough to take you off the side.
It *seems* to point towards some loss of control authority... Hydraulics - but that would take multiple failures to lose the rudder. A "nosewheel hardover"? Might explain nosewheel marks on the runway. A Flight control jam, either external or in the cockpit? Has happened before with loose items going behind the pedals and limiting travel. Where do the "rumbling noises" fit in to all of this? Normally something to do with tyres/brakes but they're apparently OK... Incapacitation - yes but I'm sure we'd have heard something by now after the debriefs.
Bit of a teaser but at least all involved survived.
What do we know so far?
* There was an RTO initiated at >100Kts.
* They reached 119kts (IAS?) before decelerating.
* After about 2,700' of roll (2,000' go, 700' stop), they left the paved surface.
* Brakes/tyres are reported as being in working condition.
* The historical METARs show a crosswind but well within limits for a dry RWY.
* "Noises off" during the takeoff roll.
* Recordings stop at 89kts after impacting a taxiway/road/earth bank.
What don't we know:
* What the RTO was commanded for - engine failure, loss of directional control, etc.
* What happened with RTO braking, reverse, spoilers, etc.
* The flying control inputs during this time.
Speculation:
I would assume that as the aircraft started to drift to the left, corrective action would have been taken (right rudder) and that would have soon gone to full deflection if the drifting continued. This is pretty much a reflex reaction for an experienced pilot and may have happened prior to the RTO decision. From the reported weather and aircraft speed at the time, there should have been no issues with Vmcg (if an engine problem) or crosswind limits. But the 737 still veered off the runway to the left...
What could have caused this?
Asymmetric forward thrust? Unlikely, as both thrust levers would have been closed during the RTO; difficult to only close one and at the speed they were at this would lead to a SE TO. Asymmetric reverse? Possible but this shouldn't cause a problem as it's factored into the limits (normal proc. for engine fail == only 1 reverser left). Uneven braking? Again, possible but I wouldn't have thought enough to take you off the side.
It *seems* to point towards some loss of control authority... Hydraulics - but that would take multiple failures to lose the rudder. A "nosewheel hardover"? Might explain nosewheel marks on the runway. A Flight control jam, either external or in the cockpit? Has happened before with loose items going behind the pedals and limiting travel. Where do the "rumbling noises" fit in to all of this? Normally something to do with tyres/brakes but they're apparently OK... Incapacitation - yes but I'm sure we'd have heard something by now after the debriefs.
Bit of a teaser but at least all involved survived.
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Nose wheel bogie?
Could these pics show the nosewheel bogey?
Links to pics as well as videos of the press briefing:
9NEWS.com | Colorado's Online News Leader | Experts to analyze recorders from charred plane
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malfunction alarms
have there been any reports of alarm sounds in the cockpit before the call for RTO?
in the scenarios being suggested would/should a warning alarm have been sounding? for example, asymetric thrust/engine fire etc?
in the scenarios being suggested would/should a warning alarm have been sounding? for example, asymetric thrust/engine fire etc?
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What could have caused this?
Local icy patch on the runway combined with a gust? Have we seen any runway friction coefficient data prior to and after the event, other than "dry"?
There are some anecdotes that hot jet exhausts could cause loose snow on the runway to melt and freeze to ice. Would affect the rotation zone where the exhausts are directed downwards. Don't know if it's pure BS or something which might only occur with afterburner heat.
Per Ardua ad Astraeus
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Things were certainly stacked up against - definitely not somewhere I would like to have been:-
apparent damage to right stab, either engine or tyre?
strong wind from the left
hi-speed RTO
you are left now with either less than full reverse on No2 (if it was engine) or autobrake RTO (if defective right gear - NTSB statement acknowledged), either adding significantly to the left yaw.
inhospitable off-piste terrain
Speedy recovery to all.
apparent damage to right stab, either engine or tyre?
strong wind from the left
hi-speed RTO
you are left now with either less than full reverse on No2 (if it was engine) or autobrake RTO (if defective right gear - NTSB statement acknowledged), either adding significantly to the left yaw.
inhospitable off-piste terrain
Speedy recovery to all.
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TheShadow said (posts 111 and 118)
.
1. "Unusual Sound"
= rolling with one main-mount tire on the port bogey deflated/underinflated/deflating - yet undetected and causing detectable vibration only latterly (once at high-speed), as it flailed, broke up and provoked a subsequent directional control issue - causing the abort (GETS MY VOTE FOR LIKELIHOOD).
This would also explain the ensuing divergence and departure from the runway.
2.
Bumping and rattling
Perhaps add to the previous conjecture that a section of loose (but not yet detached) tread on any tire can cause the sort of bumping and rattling (i.e. rotational asymmetry) that was noted during the take-off [and caused them to abort from 119kts].
.
1. "Unusual Sound"
= rolling with one main-mount tire on the port bogey deflated/underinflated/deflating - yet undetected and causing detectable vibration only latterly (once at high-speed), as it flailed, broke up and provoked a subsequent directional control issue - causing the abort (GETS MY VOTE FOR LIKELIHOOD).
This would also explain the ensuing divergence and departure from the runway.
2.
Bumping and rattling
Perhaps add to the previous conjecture that a section of loose (but not yet detached) tread on any tire can cause the sort of bumping and rattling (i.e. rotational asymmetry) that was noted during the take-off [and caused them to abort from 119kts].
Not likely to have been related to nosewheel shimmy.
Shadow's conjecture seems to be a logical sequitur to what's said in this USAToday Article:
.
The jet's tires began making marks indicating a possible skid after it had traveled 1,900 feet, Sumwalt said. It left the 12,000-foot runway after 2,650 feet, he said.
.