iberiadc852
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D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 14, 2005 3:45 am

Hello all:

I am making a little investigation about the sequence of the 1977 tenerife crash that involved a klm and a pan am 747, as most of you know.

In the D.F.D.R. it is registered the following (It is an extract of the Spanish Secretary Civil Aviation's Inform of the Crash, very interesting all it by the way).


"At 1706:46.04, i.e., 2.99 seconds before impact, increased direction toward the right is observed in the HEAD; 0.46 seconds later, a curving of the aeroplane to the left is seen in the Roll parameter (ROLL) and, 1.54 seconds before impact, a roll to the right is observed in the Roll Control Wheel Position parameter (RCW)."

As I do not understand anything about D.F.D.R's what do those registers mean?. I understand that before the impact, the KLM plane turned to both sides alternatively, right, left and right, but, were all the same type of turns?

Thanks in advance for the replies
variety is the spice of life; that's what made the "old times" so good
 
OzLAME
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 14, 2005 10:03 am

First of all, the recorded parameters of HEAD (the direction the nose is pointing) and ROLL (the angle of the wings relative to horizontal) have little or no significance so close to impact and are probably very small variations due to the KLM a/c becoming airborne. The RCW is the significant signal here; it is recording the position of the control wheel and therefore shows the crew attempting to roll the a/c to the right just prior to impact. The amount of the RCW signal may indicate that this roll command may be just to compensate for the aircraft rolling to the left. Hope this helps your understanding.
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.
 
iberiadc852
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 14, 2005 10:29 am

Thanks OzLAME, and sorry for my ignorance, but, the control wheel is the front wheel?

Anyway, I can't imagine a more significative roll that the spin of the wings around the plane's longitudinal axis, which I understand should be given by the ROLL parameter. As I am sure I am not understanding it well, could you gave a clearer vision of this?. Thank you.
variety is the spice of life; that's what made the "old times" so good
 
Newark777
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 14, 2005 11:57 am

As I am sure I am not understanding it well, could you gave a clearer vision of this?. Thank you.

As far as I understand it, roll indicates how much the aircraft is "tipping" to the right of left. So if you put a weight on the end of the wing, it would start to go down, and the roll angle would change. It really plays no part in the motion of the wheels.

Harry
Why grab a Heine when you can grab a Busch?
 
iberiadc852
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 14, 2005 5:34 pm

Quoting Newark777 (Reply 3):
As far as I understand it, roll indicates how much the aircraft is "tipping" to the right of left

Ok, that's the idea I got from OzLAME explanation. But in the moments we are talking about the KLM 747 is just getting airborne, so, which importance can have the motion of the wheels when the nose of the plane is already up and the wheels are losing contact with the ground? (It is estimated that just 1.5 sec. before the impact the KLM plane began to take off literally) Do the control wheels have something to do with the movement of the rudder when the plane is getting airborne?
variety is the spice of life; that's what made the "old times" so good
 
OzLAME
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 14, 2005 5:40 pm

Quoting Iberiadc852 (Reply 2):
Anyway, I can't imagine a more significative roll that the spin of the wings around the plane's longitudinal axis, which I understand should be given by the ROLL parameter.

You are correct, but what I should have said was the AMOUNT of roll to the left could not have been significant so close to impact, perhaps one degree, which the crew (or Autopilot?) may have been counteracting by turning the control wheel or yoke (two of which are in the cockpit, one in front of each pilot); or maybe the pilot was trying to change the direction of the aeroplane by rolling to the right at the last second (to try to avoid impacting the Pan Am a/c) and there was not enough time for the a/c to respond to the roll command. I have not seen the numbers and therefore do not know the amount of the control wheel/yoke Right Roll Command, or the ROLL or HEAD parameter changes either, but as the KLM a/c only became airborne 80 metres from the Pan Am a/c, there could not have been much change.
Monty Python's Flying Circus has nothing to do with aviation, except perhaps for Management personnel.
 
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Jetlagged
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Wed Jun 15, 2005 1:56 am

Iberiadc852, the control wheel in question is the pilot's roll control wheel (or yoke), not the undercarriage wheels. At takeoff speeds, the undercarriage wheels will hardly give any directional control at all.

The pilot's wheel controls the ailerons and roll spoilers, and so roll angle in flight. It's not a lot of use on the ground, except to counter crosswind effects. If the aircraft heading drifted to the right just before lift off, the roll angle would tend to go left in reaction. The pilot's instinctive reaction would be to pick the wing up with right control wheel input. To avoid the PanAm aircraft they would be pulling up (column fully aft). Turning left or right would have no real effect on the outcome and would actually a cause a loss of lift.

OzLAME, The autopilot would not have been engaged during takeoff under any circumstances.
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iberiadc852
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Wed Jun 15, 2005 5:14 pm

Thanks a lot to both, now I understand it quite better. Yes, I know there should be some values, but I haven't got them now, I am not sure if have seen them some time ago. And yes, Jetlagged, I found it hard to believe that it was the front undercarriage wheel, but that was the quickest way to ask about my doubts; anyway, in that case the only possible (though odd) explanation for me was it could indicate a rudder movement; do front wheels move with the rudder when the nose of a plane is pointing up?. (I suppose not, but now my curiosity has waken up about it, since that should be implemented; actually I am just supposing they move as one in ground, but my only "source" for that is Flight Sumulator)

And, OzLAME, where do you know from the KLM became airborne so much? And from which part of the plane are the 80 meters supposed to be measured?

Thanks again
variety is the spice of life; that's what made the "old times" so good
 
tbanger
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Wed Jun 15, 2005 6:16 pm

Quote:
Iberiadc852 Reply 7

do front wheels move with the rudder when the nose of a plane is pointing up?. (I suppose not, but now my curiosity has waken up about it, since that should be implemented; actually I am just supposing they move as one in ground, but my only "source" for that is Flight Sumulator)

The nose wheel steering on larger aircraft are controlled with a tiller. This is like a little wheel that the pilot uses to steer the nose wheel. It is not linked to the rudder, nor is the rudder pedals linked to the nose wheel steering.

Your hand can fit over the tiller and needs to be pushed down so as to engage the steering mechanism. As soon as you let your hand off it, it springs up and the nose wheel will caster.

since that should be implemented;

At any speed above about 80kts, the nose wheel steering will have absolutely no effect on the aircraft direction.... The rudder takes over here.
 
Vain~
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Wed Jun 15, 2005 11:53 pm

Quoting Tbanger (Reply 8):
nor is the rudder pedals linked to the nose wheel steering

This depends on aircraft type, on the B737 the rudder pedals are linked to the nose wheel steering when the aircraft is on the ground, with rudder pedals you can get the nose wheels to 7 degrees to either side. Don't know about the 747, but probably similar

Quoting Tbanger (Reply 8):
Your hand can fit over the tiller and needs to be pushed down so as to engage the steering mechanism. As soon as you let your hand off it, it springs up and the nose wheel will caster

Never seen this on boeings, tiller always connected, with airplane on ground
nose gear will automatically center when airborne.
 
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Jetlagged
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Sun Jun 19, 2005 2:57 am

Quoting Vain~ (Reply 9):
This depends on aircraft type, on the B737 the rudder pedals are linked to the nose wheel steering when the aircraft is on the ground, with rudder pedals you can get the nose wheels to 7 degrees to either side. Don't know about the 747, but probably similar

Pedal steering was usually installed on the 747 Classic but could be disabled as a customer option. Most airliners have limited nosewheel steering authority via the rudder pedals. From memory, the Fokker F.28 is one of the few which doesn't.
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jeb94
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Sun Jun 19, 2005 4:50 pm

The DC9 family will get 17 degrees right or left nosewheel steering from the rudder pedals with the aircraft on the ground. With the nose strut fully extended (airborne) there is a cam inside the strut that centers and locks the nosewheels so they won't turn. I can't be 100% sure as I've never worked on a 747 but I believe it has something similar in its strut. With the nosewheel airborne its locked straight forward.
 
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Jetlagged
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Sun Jun 19, 2005 9:26 pm

It's standard on all nosewheel struts for the wheel to be centered automatically by a cam as the strut extends. This applies to castoring as well as steerable nosewheels.

Once the wheel has left the ground it's not going to be doing any steering and needs to be fore and aft for retraction into the wheel well.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
geoffm
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Mon Jun 20, 2005 4:51 am

Quick question about the accuracy of the DFDR. Twenty-eight years ago computer technology (or even recording technology) wasn't that advanced. So can they really claim an accuracy of 0.01 seconds on an event happening? How many samples a second would they have had in those days - and how many these days (typically)?

Geoff M.
 
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Jetlagged
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RE: D.F.D.R. Question About The KLM/PANAM Crash

Tue Jun 21, 2005 9:25 pm

With a digital recorder you can only have time accuracy down to the sampling rate. However if the sample rate is accurate, the time is at least accurate in a relative sense. With simple analogue systems, sampling rate is irrelevant (recording is continuous). Timing accuracy is dependent on how well the speed of the recording medium is controlled (probably not that accurate then). However if the analogue data is multiplexed then the cycle time for the multiplexer is a factor too.
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