Hard landing / severe turbulence ?

[jettison valve]

Good evening,

We´ve been running into some strange situations concerning hard landings / severe turbulence lately - and the way how to deal with them. In this frame, I have the following questions :confused: for you:

- With long and less stiff airplane structures (e. g. A340-600), does the flight crew still have a reliable feeling / indication of a hard landing and/or severe turbulence (I am not talking about sink rates at touchdown here)? As of today, the flight crew report is the trigger to start an inspection... :uhoh:

- How do you match FOQA data with ACMS data (load report), especially when the AMCS and the flight crew did not report anything while FOQA later on apparently "detects" an excessive load?

- Having scratched my head over the interpretation of A340 load reports quite a few times last year :ugh: , I wonder if we cannot get more reliable aircraft system data in the future:
RVDTs/proximity sensors/pressure sensors on the landing gear detect the actual touchdown time, three axis accelerometers in the centre wing section detect hard landings (accelerometers in the tail can contribute to turbulence data). Data acquisition and storage in approx. 0.1s intervals should be feasible to allow proper assessment of the landing / turbulence. Is it too far fetched?

Looking forward to your comments! :ok:

Cheers,
J. V.

[kichwa tembo]

Sorry jettison, I don't have an answer for you, but with your permission a question.

How do FOQA and FDA systems detect G inflight and on landing? Are there accelerometers in the structure purely for this function?

[BOAC]

I have always assumed they would use the vertical axis accelerometer in the IRS/INS system.

[safetypee]

My experience of attempting to correlate touchdown ‘g’ with a ‘heavy landing’ in regional aircraft – using older FDR/sensors, would suggest that great care has to be taken if you are to avoid constraining an operation. The FDR touchdown ‘g’ was a poor guide to a heavy landing which involved the structure – this always required a visual inspection.

I recall that the FAA conducted tests which involving filming routine landings, some at LCY. (FAA Atlantic City division) I will search my archives.

For the less erudite then the obvious option is to avoid those situations that might result in a heavy landing; see the briefings under the Approach and Landing Techniques. ( www.airbus.com/en/corporate/ethics/safety_lib/index.html)

[Roadtrip]

A hard landing is a subjective determination by the PIC.

[dusk2dawn]

Thats why there are so few of them ;)

[spannersatcx]

I have always assumed they would use the vertical axis accelerometer in the IRS/INS system.

Never Assume as you know what they say it makes.....:)

The 340-600 and other 340's have a 3 axis accelerometer that feeds into the DFDRS system.

The 747 also has accelerometers fitted for a similar purpose. :)

[BOAC]

......and you are saying they are NOT part of the IRS/INS system, but separate accelerometers for assessing landings?

[mustafagander]

Back in the "Good Old Days" the DC8 50 series (and maybe other DC8s) had a thin Al strip attached to the lower edge of the MLG oleos, pointing up. Part of the T/R check for the LAME (me) was to check the strip was not bent. Strip bent = hard landing, inspection required - strip not bent landing OK, well structurally at least.

I am at a complete loss as to why modern types do not use such a simply system to help monitor hard landing. BTW we nicknamed the strips "lie detectors". :ok:

[spannersatcx]

......and you are saying they are NOT part of the IRS/INS system, but separate accelerometers for assessing landings?

Yes:) they are inputs to the FDRS and can be accesses through the ACMS. We would also pull the QAR disk/tape and get those read as well.

346 AMM - ACMS function: The DMU part receives the necessary data from the aircraft systems and monitors these continuously. Occurs a specified condition or event the FDIMU automatically starts a pre-programmed Report. The FDIMU stores the result of this report on the internal non-volatile solid-state mass memory (SSMM). The report with their result can also be recorded either on the internal Smart ACMS Recorder SAR or on the PCMCIA card (if installed) or on the external Digital ACMS Recorder DAR (if installed). The SAR storage medium is a part of the SSMM. The user can make a printout of the on the SSMM stored Reports. In addition the Reports can also be transmitted to the ground station through the ATSU (ACARS) or downloaded through the MDDU or PCMCIA card.

The system software consists following standard Reports:
For Aircraft Performing Monitoring:
- <02> Aircraft Cruise Performance Report
- <50> Cruise Stability Statistic Report
For Engine Trend Monitoring:
- <04> Engine Take-Off Report
- <01> Engine Cruise Report
- <09> Engine Divergence Report
- <08> Engine Reverse Report
For Engine Exceeding Monitoring:
- <10> Engine Start Report
- <06> Engine Gas Path Advisory Report
- <07> Engine Mechanical Advisory Report
For Trouble Shooting:
- <11> Engine Run-Up Report
- <05> Engine On Request Report
For APU Monitoring
- <13> APU Main Engine Start / APU Idle Report
- <14> APU Shut Down Report
For Miscellaneous Monitoring Functions:
- <15> Hard Landing / Structural Load Report
- <19> Environmental Condition System Report
- <20> Ram Air Turbine Test Report
- <21> Door and Escape-Slides Control System Report
- <16> User Programmable Report
- <17> User Programmable Report
- <18> User Programmable Report

AMM 31-33-00 -
The three-axis Linear Accelerometer (LA) is installed between Frame 46 and 47 under a floor panel of the passenger compartment (center of gravity of the A/C). The LA generates acceleration data in analog format. The analog information from the LA is sent to the System Data Acquisition Computer (SDAC). The SDAC converts this information to a digital format and sends it via an ARINC-429 data-bus to the FDIU-part. The FDIU-parts sends these acceleration data to the DFDR together with the other flight-parameters. On each flight the FDIU-parts makes an integrity check of the acceleration-parameters.

[BOAC]

Could you just run that past me again....................:) :)

I am just surprised that you need longitudinal and lateral acceleration for maintenance monitoring and do not use the on-board 3-axis acceleration monitoring system built into the IRS/INS, but so be it.

[CaptainProp]

If you would exceed any limitations such as G´s for landing, VFEs etc you will get an aut printout. No need for bright pilots to assess landings!!:p Print out - Oooops! No print out - Phu, beer is on me!;)
/CP

[Checkers]

Well, on most aircraft there is a three-axis accelerometer that is a dedicated part of the flight data recording system. I think on Airbii, the recorded acceleration might be the same data source used by the flight control system.

A hard landing can be defined several ways ... vertical load factor at touchdown, which can be subject to aliasing due to a slow acquisition rate (relative to the near-impluse loading of a brusque landing) or vertical speed close to touchdown, which has is own problems because of ground effect on the pitot-static system if IVV isn't available or if there is varying terrain short of the threshold (trying the RALT rate).

There is also a whole host of contributing factors that could be examined for correlation ... was the approach flown particularly far from Vapp, was it a navy-style landing, did the landing balloon, was the descent gradient steep, etc?

Ultimately, you're probably going to be diappointed if you rely on any one data source (including crew reporting) to accomplish the goal of avoiding unwarranted maintenance time for inspections or flying around with a damaged aircraft

[ChristiaanJ]

I am just surprised that you need longitudinal and lateral acceleration for maintenance monitoring....Since they feed into the FDR, I doubt they are there just for maintenance purposes.

And thinking back to the famous Kai Tak videos..... I do think you may want all three axes.

[Oldy]

I am probably being too simplistic. But we used to use the worst case of pilot reports and aircraft monitoring systems. Neither are perfect.

[jettison valve]

Gents (any female ppruners here??? :confused: ),

Thanks for your replies so far.

Roadtrip
It´s today´s understanding that the PIC decides whether it was a hard landing, I agree.
However, we know that this is unreliable (as also current aircraft systems that should decide this issue!).

Mustafagander
AI just suggested replacing a link on the A346 landing gear with an indicator strip. Looks like this is a) unreliable and b) causes landing gear overhauls which may not be necessary in fact... :ugh:

Spannersatcx
You are correct in your elaboration. However, one cause for inaccuracy is the radio altimeter rate: With the RA being firmly installed on the fuselage, changes in pitch attitude have an effect on RALR, which is apparently not fully compensated by ADIRU data for instance.
The deeper I dig the more I get pessimistic in this issue... :{

CaptainProp,
Wrong. Several (Airbus operating) airlines have deactivated auto-printout (while still storing the data!) because of poor reliability of the triggers. They were fed up with delays and useless inspections...

Checkers,
I fully agree - unfortunately. :{

Oldy,
I can tell you from last year´s experience, we would have got the A340 off the ground not too often on-time with the vast amount of "<15> Hard Landing / Structural Load Reports" :uhoh: But that was also due to a misprogrammed FDIMU...:ugh:

----
Interestingly, no one has adressed question 1 (flight crew setting the trigger for hard landing / severe turbulence) in detail.
Bearing in mind the AA A300 crash in New York and the recent changes in the Maintenance Manuals concerning severe turbulence, what makes you report a flight through heavy turbulence (and a hard landing)? Your personal perception, cabin crew reports, sinkrate, looking into aircraft data yourself...?

Cheers,
J.V.

[Oldy]

JV,

In aswer to your question "what makes you report a flight through heavy turbulence (and a hard landing)? Your personal perception, cabin crew reports, sinkrate, looking into aircraft data yourself...?"

I always used to use myself and advise the following to my colleagues:-

If on a subsequent flight the aircraft suffered structural damage and hurt /killed someone because you had failed to notify maintenance personnel of an event on your own flight you would not be able to sleep at night and may not be able to live with yourself afterwards. ALWAYS tell it how YOU see it as the commander. It is subjective I know, but there you are. Of course the commander should use his/her professional judgement from all sources - reports from other crew as well as electronic sensors. He/she is far better placed than maintenance personnel to make this judgement purely from the fact that they were there at the time.

Incidently this thought process applies to more than turbulence and heavy landings.

[captain_jeeves]

Maybe this will help the turbulence part of the question.

I got these references to "Chop and Turbulence" from an Aerospace Engineering Text-book a number of years ago. They have proven consistent over the years with the "Walking around the cabin" definitions, and I figure if the Engineers are building them to these values, they should be reasonably accurate.

Obviously, all speeds and rates are indicated values.


Light Chop
5 - 14 kts of airspeed change only

Moderate Chop
15 - 25 kts of airspeed change only

Light Turbulence
5 -14 kts of airspeed change AND 300-1199 feet Vertical Speed Change / Min

Moderate Turbulence
15-25 kts of airspeed change AND 1200-2099 feet Vertical Speed Change / Min

Severe Turbulence
+25 kts of airspeed change AND 2100 - 2999 feet Vertical Speed Change / Min

Extreme Turbulence
+3000 FPM feet Vertical Speed Change / Min

[rhovsquared]

Captain_Jeeves: thanx you'd also inadvertantly assisted me on a problem that's been troubling me;)


CRI-VOR/DME Inop :D :D :D
rhov:)

[captain_jeeves]

Captain_Jeeves: thanx you'd also inadvertantly assisted me on a problem that's been troubling me;)


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