United Overweight Takeoff on Computer Mistake Prompts Changes

[At ease]

Quote:
You'd also need to factor in shock strut pressure

Right. And don't forget the static friction in the strut seals.

Having been no closer to main oleo's on a "heavy" than the seats over the wing(as SLF), can any aircraft engineer give me a general idea of the maximum travel or "stroke" of a large aircraft oleo(only when on the ground , of course)?

Manufacturers of automotive struts/dampers such as Bilstein/KYB provide such information on request and/or on the www. for their products.

I imagine aerospace strut manufacturers(MessierDowty - Goodrich ??) would have such information available to those "with a need to know".

Unfortunately, I am not one of those with such a need.

Can any one help?

Data relating to a 737-900(the subject of this thread) would do nicely.

Ta.

[Dairyground]

Measuring mass directly or indirectly, whether by weight pads, lg strain, light or radio echo timing, or even Dam Busters-style triangualtion could be useful and would probabably pick up the recent United case, but would not detect the EK Melbourne case, where mass was known but the wrong value was entered into the TO calculations.

What is needed is something de-coupled as much as possible from information capture and data entry processes.

Various critical speeds, the V-speeds, are calculated on the basis of aircraft mass and other factors. Most of these other factors are reasonably well established, such as runway characteristics, including length. The only doubtful value is the mass entered into the calculation. Bad mass gives you bad V1 and V2.

However, the calculation can easily be adapted to give the time needed to accelerate from brakes off to any or all of thr v-speeds, or indeed any other speed.

In the EK melbourne thread I suggested that time to V1 could be used as a gross check on the mass and other inputs to the performance calculation. Nobody, as I recall, suggested that the concept would not work, but there were assertions that monitoring time to speed would be vert difficult to include in the process at a very busy time for the flight crew. I am not convinced that something along these lines would not be possible. Time to some speed lower than V1 might be better than V1 (cooler brakes if you decide to stop) and an automated "drop the anchors" rather than PNF having his eyes on a stopwatch could mitigate some of the workload concerns.

[Arfur Dent]

DP Davies in 'Handling the big Jets' (essential reading for Cathay entrants many years ago') said 'The Captain of a 747 should know his aircraft's weight to the nearest 10 tons!'
Aircraft performance is pretty 'on side' with all the assumptions we make - that's why the 737 subject aircraft and crew survived. Gross error checks are one thing but we can't go down the cabin and weigh everyone as their final abuse before getting airborne - can we?

[DaveReidUK]

Nobody, as I recall, suggested that the concept would not work, but there were assertions that monitoring time to speed would be vert difficult to include in the process at a very busy time for the flight crew. I am not convinced that something along these lines would not be possible.

In the age of ADS-B, where pretty well every commercial aircraft on the runway broadcasts its velocity twice every second and acceleration can be readily derived, I'm surprised that the possibility of an externally-monitored safety-net isn't being considered.

[hetfield]

In the age of ADS-B, where pretty well every commercial aircraft on the runway broadcasts its velocity twice every second and acceleration can be readily derived, I'm surprised that the possibility of an externally-monitored safety-net isn't being considered.

AFAIK update rate is one per second.

Don't think ADS-B is a solution for impropper performance calculations. ADS-B relies on GS (time delay!), performance on airspeed.

[DaveReidUK]

AFAIK update rate is one per second.

Nope, definitely twice per second. But even if you only take every other transmission, you would still have more than enough data points to produce a pretty decent acceleration curve.

Don't think ADS-B is a solution for improper performance calculations. ADS-B relies on GS (time delay!), performance on airspeed.

I think you're missing the point. Of course the wind on the nose affects the relationship between groundspeed and airspeed, and hence aerodynamic performance.

But that's not what we're talking about here. Instead, we're using Newton, rather than Bernoulli - i.e. initial takeoff roll acceleration as a proxy to deduce aircraft mass (for a given assumed thrust).

[The Ancient Geek]

Why bother deriving mass ?.
All you need to know is that the acceleration is adequate to achieve V1 and have room to stop within the available distance.

All you need is an accelerometer and a database of runway lenths.
It would be a good idea to take the runway lenth from precision GPS which would cater for cases of wrong runway, intersection and taxiway foulups.

One cheap and simple piece of technology neatly covering all of the major risks with no need for error prone pilot inputs.

If the magic box yells ABORT you obey and figure out why before trying again. The cause might be overweight but there are many other potential causes, all covered.

Always remember the KISS principle - Keep It Simple Stupid.

[ColinBJ]

Mass is still relevant, because if your mass is higher than you expect, not only will your acceleration be lower, but your safe takeoff speed will be higher - a double whammy.

[Vulcancruiser]

Used the UAL system for 15 years.......

I have so much to say here but will keep it zipped for the good of the industry. 99.9% of the Atp's should have caught this before it was any factor at all with a simple check, which you can be sure UAL has now added to the manual. We can all just give a nod of the hat to Bill Boeing and happily go whistling down the street.

I still get a chuckle recalling a story told to me years ago by an A320 FO. He said he had worked his way up through the ranks the hard way. He was once a freight dog down in the Caribbean on a DC-3 outfit. His first day on the job the left seater informed him his job was to go back to the tail wheel shock and keep an eye on it. They would fork in freight until the rear shock compressed to the width of four fingers!........that was the weight and balance.......lol.........I miss the old days..........

[Reinhardt]

Some French aircraft have acceleration displayed during take-off roll - so just check value at 60 kts, mentally compare with the one you prepared before and which is written down on the take-off card... relatively easy.
Then now people can make mistake in the calculation of that desired acceleration, the same way they would do for the other values !
Believe it or not, a reason against using acceleration for performance checks, is the number of pilots uncomfortable with the picture, and how it works. Speed, weight and time is usually enough for so many colleagues... if you don't believe, check people around.
Same thing for deceleration when talking about landing : how many can write down the couple of physical formula by heart - and use them ?

[Mimpe]

One friend of mine flying an Airbus for Qantas mentioned the other day he tends to routinely add about 6 degrees C to the temperature on the data input just to add an extra layer of safety. Probably not SOP but it sounds healthy!

[RoyHudd]

Gross Weight indication

Gross Weight is indicated on the A320/330/340/380. Permanently.

You have to be a nincompoop (Emirates Melbourne example) not to use this displayed weight as a cross-check for weight inserted into perf calculations and against the loadsheet. My company use it for TO trim calcs too.

This is important stuff.