NW A320 tailstrike at DEN, possible W/O?
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NW A320 tailstrike at DEN, possible W/O?
Looks like NW had a rough landing at DEN resulting in a tail strike on
an A320 and possible W/O of the aircraft.
Pretty hard landing with a 3.G+ force applied
JACDEC - Current News
an A320 and possible W/O of the aircraft.
Pretty hard landing with a 3.G+ force applied
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3.5 G landing, things may have changed, but we were taught in the Air Force, that G meters do not read correctly on the ground.
Is that still the case.
Is that still the case.
I couldn't tell from my read if the G reading was before or after it hit he ground. It does make a difference.
Last edited by lomapaseo; 9th May 2009 at 17:44.
lomapaseo;
In flight data analysis, 'g' is usually sampled at pretty high rates. The 320 LFL (logical frame layout - the software "frame", something like a spreadsheet, into which data is recorded) records 'g' at 8x per second. The DFDR (crash recorder) on the 777 records 'g' at the same rate but our LFL for the 777 records it at 10x per second.
UDRI, the University of Dayton Research Institute with whom I and others have collectively worked in the past, does a very wide-ranging loads analysis program on different airframes including the 777. They wrote a paper a while back discussing the reliability of the 'g' parameter on the Boeing 777 because of the sensors' location in the cockpit area, (IRS's), instead of near/at the center of gravity of the airplane*. We concur with that finding, (no formal communications with UDRI - it's a known issue for the Boeing).
The reading and interpretation of flight data requires considerable "time in". What can appear a "holy cow", can in fact be a non-event. The reverse can also be true.
The Airbus 'g' parameter is 99% reliable in my experience although, like any data, it can in rare occasions exhibit a spike or two. The way to read the parameter, (which is obvious if one thinks about it), is to see what the readings before and after the highest reading are doing.
A "3.5g" reading does not occur in one-eighth of a second - it will have a "ramp up", "ramp down" of readings in the previous and post samples even if it occurs over a half-second, (four readings).
I have seen such readings and before apprising anyone we ensure that such readings are valid, using this and other techniques such as interpreting the IVSI parameter. Anything over 6fps (about 340fpm) usually results in a hard landing. We also look at the rate of change of the radio altimeter which is also sampled at between four and eight times per second, (the 777 has 3 radio altimeters and parameters).
Interestingly, the 777 AMM states very clearly that the pilot must first report a hard landing (or any other aircraft limitation exceedance) before maintenance action will take place. Once reported, the 777 has the usual limits which are then examined in the DFDR or QAR to determine what kind of hard landing check is required. In other words, if it is not reported by the pilot, it didn't happen. The Airbus philosophy is substantially different, where data is an integral part of the operation. I do not know why these differences obtain and do not wish to spark an AB "discussion". The one difficulty inherent in waiting until a pilot reports an airframe exceedance however is, such an exceedance is always available and known through the daily flight data analysis by the safety department personnel but, because of the way the 777 AMM is written, even though there may be significant exceedance indicated in the data, the operator is not required to do anything about it. For many including myself, there are inherent ethical, legal and technical issues outstanding in this approach now that data analysis is becoming not only routine but mandated under SMS.
Also, there is in place, a mistaken impression, principally from operations and maintenance personnel, probably not intentional of course, that views "QAR" data as somehow "inferior" to DFDR data and so can be safely dismissed when/if commercially inconvenient, as "advisory" only. QAR data is the same kind of peripheral as the DFDR and receives exactly the same digital data from the ARINC 429, 617 etc databusses that the DFDR does. If the data is bad for the QAR, then it is likely bad for the DFDR in which case there could be a pending legal issue. The prevalence of this view (that QAR data is "not valid"), is a regulatory matter and not merely an airline SMS issue. Anyway, enough thread drift - the 'g' readings on this 320 are almost certainly accurate, having seen them and analyzed them in other cases. If I recall, a "3.5" g reading exceeds 320 airframe certification limits by at least 1g if not 1.5g's.
-------------------------------------
* From the Abstract:
The B-777 airplane sensors, which measure vertical, lateral, and longitudinal acceleration, are located in the cockpit area. The estimates of the center of gravity (c.g.) accelerations are computed in the Air Data Inertial Reference Unit, which converts the measured crew station accelerations to accelerations at the c.g. For some dynamic and ground load conditions, inaccuracies could exist in these filtered c.g. time history measurements. Operators and inspectors who use the recorded B-777 acceleration values as maintenance action triggers or Flight Operational Quality Assurance events should recognize the possibility of recorded Digital Flight Data Recorder acceleration inaccuracies.
I couldn't tell from my read if the G reading was before or after it hit he ground. It does make a difference.
UDRI, the University of Dayton Research Institute with whom I and others have collectively worked in the past, does a very wide-ranging loads analysis program on different airframes including the 777. They wrote a paper a while back discussing the reliability of the 'g' parameter on the Boeing 777 because of the sensors' location in the cockpit area, (IRS's), instead of near/at the center of gravity of the airplane*. We concur with that finding, (no formal communications with UDRI - it's a known issue for the Boeing).
The reading and interpretation of flight data requires considerable "time in". What can appear a "holy cow", can in fact be a non-event. The reverse can also be true.
The Airbus 'g' parameter is 99% reliable in my experience although, like any data, it can in rare occasions exhibit a spike or two. The way to read the parameter, (which is obvious if one thinks about it), is to see what the readings before and after the highest reading are doing.
A "3.5g" reading does not occur in one-eighth of a second - it will have a "ramp up", "ramp down" of readings in the previous and post samples even if it occurs over a half-second, (four readings).
I have seen such readings and before apprising anyone we ensure that such readings are valid, using this and other techniques such as interpreting the IVSI parameter. Anything over 6fps (about 340fpm) usually results in a hard landing. We also look at the rate of change of the radio altimeter which is also sampled at between four and eight times per second, (the 777 has 3 radio altimeters and parameters).
Interestingly, the 777 AMM states very clearly that the pilot must first report a hard landing (or any other aircraft limitation exceedance) before maintenance action will take place. Once reported, the 777 has the usual limits which are then examined in the DFDR or QAR to determine what kind of hard landing check is required. In other words, if it is not reported by the pilot, it didn't happen. The Airbus philosophy is substantially different, where data is an integral part of the operation. I do not know why these differences obtain and do not wish to spark an AB "discussion". The one difficulty inherent in waiting until a pilot reports an airframe exceedance however is, such an exceedance is always available and known through the daily flight data analysis by the safety department personnel but, because of the way the 777 AMM is written, even though there may be significant exceedance indicated in the data, the operator is not required to do anything about it. For many including myself, there are inherent ethical, legal and technical issues outstanding in this approach now that data analysis is becoming not only routine but mandated under SMS.
Also, there is in place, a mistaken impression, principally from operations and maintenance personnel, probably not intentional of course, that views "QAR" data as somehow "inferior" to DFDR data and so can be safely dismissed when/if commercially inconvenient, as "advisory" only. QAR data is the same kind of peripheral as the DFDR and receives exactly the same digital data from the ARINC 429, 617 etc databusses that the DFDR does. If the data is bad for the QAR, then it is likely bad for the DFDR in which case there could be a pending legal issue. The prevalence of this view (that QAR data is "not valid"), is a regulatory matter and not merely an airline SMS issue. Anyway, enough thread drift - the 'g' readings on this 320 are almost certainly accurate, having seen them and analyzed them in other cases. If I recall, a "3.5" g reading exceeds 320 airframe certification limits by at least 1g if not 1.5g's.
-------------------------------------
* From the Abstract:
The B-777 airplane sensors, which measure vertical, lateral, and longitudinal acceleration, are located in the cockpit area. The estimates of the center of gravity (c.g.) accelerations are computed in the Air Data Inertial Reference Unit, which converts the measured crew station accelerations to accelerations at the c.g. For some dynamic and ground load conditions, inaccuracies could exist in these filtered c.g. time history measurements. Operators and inspectors who use the recorded B-777 acceleration values as maintenance action triggers or Flight Operational Quality Assurance events should recognize the possibility of recorded Digital Flight Data Recorder acceleration inaccuracies.
Last edited by PJ2; 9th May 2009 at 17:43.
PJ2
Agree with everything that you wrote
However my intrpretation of the quote below, that I replied in my post has to do with not the gross inflight acceleration changes (acting over a large body) but the unique decelleration loads near the G sensor once crushing has occured
[quote] 3.5 G landing, things may have changed, but we were taught in the Air Force, that G meters do not read correctly on the ground.
Is that still the case. /quote]
Agree with everything that you wrote
However my intrpretation of the quote below, that I replied in my post has to do with not the gross inflight acceleration changes (acting over a large body) but the unique decelleration loads near the G sensor once crushing has occured
[quote] 3.5 G landing, things may have changed, but we were taught in the Air Force, that G meters do not read correctly on the ground.
Is that still the case. /quote]
lomapaseo;
I guess we'd need to know what kind of 'g' meter - mechanical or electronic, instantaneously reading or capturing data over time, or whether it just reads the highs (or lows).
In the 'g' data I've read, you can see the 'g' reading "climb" over a one second sample such that it forms a rough "bell curve" in a graph plot. Data that is suspect, instantly spikes to, say, 2.6, with no lead-in/lead-out readings.
So I can't really comment on military 'g' meters as I have no experience with them nor do I know how they work at landing but, notwithstanding the 777 issues with the 'g' reading, the Airbus readings are reliable in all phases of flight including on the ground, (where the vertical parameter is used to determine rough runways and the lateral parameter, high speed turns causing high lateral loads on the gear), and it is easy to spot spikey data and dismiss it as false. I can tell you that single-engine taxiing for example, will spike the 'g' parameter when the generator comes on/falls off line. It's just part of the interpretive work.
I guess we'd need to know what kind of 'g' meter - mechanical or electronic, instantaneously reading or capturing data over time, or whether it just reads the highs (or lows).
In the 'g' data I've read, you can see the 'g' reading "climb" over a one second sample such that it forms a rough "bell curve" in a graph plot. Data that is suspect, instantly spikes to, say, 2.6, with no lead-in/lead-out readings.
So I can't really comment on military 'g' meters as I have no experience with them nor do I know how they work at landing but, notwithstanding the 777 issues with the 'g' reading, the Airbus readings are reliable in all phases of flight including on the ground, (where the vertical parameter is used to determine rough runways and the lateral parameter, high speed turns causing high lateral loads on the gear), and it is easy to spot spikey data and dismiss it as false. I can tell you that single-engine taxiing for example, will spike the 'g' parameter when the generator comes on/falls off line. It's just part of the interpretive work.
Last edited by PJ2; 9th May 2009 at 18:10.
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PJ2,
Are you saying that the G trace the FDR gets comes from the IRS in the 777? that's a weird setup, most of the aircrafts that I'm familiar with have a dedicated accelerometer for the FDR, and it's located more or less near the A/C CG....example: CRJ, Cl 605 etc.... By the way, the CL605 has dual IRS.
Before I forget, thanks for posting a link to that document, I started reading it and it's quite interesting.
Are you saying that the G trace the FDR gets comes from the IRS in the 777? that's a weird setup, most of the aircrafts that I'm familiar with have a dedicated accelerometer for the FDR, and it's located more or less near the A/C CG....example: CRJ, Cl 605 etc.... By the way, the CL605 has dual IRS.
Before I forget, thanks for posting a link to that document, I started reading it and it's quite interesting.
Bottums Up
I currently fly a Douglas/Boeing 717 that was repaired by the Boys from Boeing, after a 3.2 G heavy landing. They said it wasn't as damaged as some they'd seen.
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On the Airbus aircraft, the engine flight idle increases to "approach idle" setting, based on flap selection (i.e. Flap 1 on the A320 family) or the selection of landing gear down (widebodies). From the depths of my memory this is to comply with FAR 33.73 engine idle to 95% of take off thrust spool up time requirements.
Perhaps someone can take us through how this relates to the FAA 8900.1 order as cited by IGh?
If the approach idle setting on the Airbus aircraft meets FAR 33.73 requirements does that mean that it complies with FAA 8900.1 or do we need to have a higher minimu thrust setting? IF we do what is the minimu setting to be in compliance with FAA 8900.1?
Perhaps someone can take us through how this relates to the FAA 8900.1 order as cited by IGh?
If the approach idle setting on the Airbus aircraft meets FAR 33.73 requirements does that mean that it complies with FAA 8900.1 or do we need to have a higher minimu thrust setting? IF we do what is the minimu setting to be in compliance with FAA 8900.1?
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IGh, thanks for the detailed and informative reply. So far trolling through the Airbus FCOM's provides no clear answer on what that minimum thrust setting is to be in compliance with FAA 8900.1. I checked the manufacturer's document and a few airline specific ones.
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I can attest that N311US, the NW Airbus that carries some distinction as it wears the Delta colors, has been sitting in DEN for the past month and hasn't moved one inch (or centimeter) from its hardstand (just north of and adjacent to Twy CN) during that time period.
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Reporting or not
I recall in SFO on or about 1 Mar 2004 a DL 757 taxiing to the gate on Alpha was hit by a fuel tanker. #2 engine was totally trashed. No report ever on the NTSB site, someone must have some powerful mojo. I have pictures somewhere.
SB
SB
IGh,
No, the standard landing flap setting is known as "Flaps FULL".
In my day (1988-2001), Flaps 3 was recommended in turbulence, windsheer, and/or limiting crosswind. Many of us, however, found this unsatisfactory, mainly because of the FBW handling characteristics. (Flaps 3 is also a take-off setting, and this somehow affected them; there may have subsequently been a software fix.) The other slight disadvantage was the lower thrust setting, and the unfamiliar (higher) pitch-attitude (sorry, deck-angle!).
In the early days, before the double-acting L/G shock-strut was introduced, the only reliable way to get a 'greaser' involved an excessive amount of floating along a (long) runway. But I don't remember any of us doing a tail-strike... Needless to say, the latter would be more likely at Flaps 3.
Chris
No, the standard landing flap setting is known as "Flaps FULL".
In my day (1988-2001), Flaps 3 was recommended in turbulence, windsheer, and/or limiting crosswind. Many of us, however, found this unsatisfactory, mainly because of the FBW handling characteristics. (Flaps 3 is also a take-off setting, and this somehow affected them; there may have subsequently been a software fix.) The other slight disadvantage was the lower thrust setting, and the unfamiliar (higher) pitch-attitude (sorry, deck-angle!).
In the early days, before the double-acting L/G shock-strut was introduced, the only reliable way to get a 'greaser' involved an excessive amount of floating along a (long) runway. But I don't remember any of us doing a tail-strike... Needless to say, the latter would be more likely at Flaps 3.
Chris
Last edited by Chris Scott; 13th Apr 2010 at 18:08. Reason: Last sentence added.
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Clearly this event is also no stranger to the "Evolution of Ground Spoiler Logic" as described in the Airbus Safety Magazine Edition February 2010. (Thanks fredgrav )
Also, and if still needed, this is another example how a dual input is the natural answer to a degraded situation. Or when the L/R side don't know what the opposite side is doing ... !?
Don't blame the crew here, but the system.
)Also, and if still needed, this is another example how a dual input is the natural answer to a degraded situation. Or when the L/R side don't know what the opposite side is doing ... !?
Don't blame the crew here, but the system.