Getting landing G from the FMC
 

Hi all,

I recall hearing somewhere that there was a way to get the landing G value from the FMC for the 737 NG. Does anybody here know the trick?

Thanks,

Dinshaw.

Sorry but what is landing G?

The G force value. G stands for Gravity. 1G= force of gravity. In simple terms it is used as a convenient measure of the loads on an aircraft.

menu-> acms -> display -> alpha -> VGTD into box prompts

(vertical G's touch down)

not sure about the steps "display" and "alpha". but you're gonna find it.
try also VGMN (min) VGMX (max)
there is also a long list in the acms of pretty much all paramters....

Hey FCS Explorer, thanks a lot. Will give it a shot. Much appreciated.

question??
 

can pilots access this info? and for how many cycles previous does the info appear for?

cheers

Just a quick cautionary note: that value is almost certainly be sampled at a relatively low rate, and as such the true peak load may well be missed. Other factors also come into play in assessing the degree of 'hardness' of a landing too (one gear or two, sideload or not, etc.) so I'd be careful about relying too much on that single piece of data.

Well, on the older B767 system I've seen, the G load is sampled 8 times per second. I can't see why the NG wouldn't be at least the same or even greater.

On our 733's we get a post flight print out which includes min and max VG and also a land VG. Have been told though that the land VG is sampled from the nose gear, so just ease the nose down to ensure you don't have to pay for the first beer at the hotel :8

@JO

8 Hz is the required FDR rate, IIRC, so that's about the rate I'd expect most systems to work at. And it's not fast enough to capture a peak for something like a hard landing unless the sample happens at just the right time - 1/8 second is a long time to wait when you're trying to measure an impact.

You can get a full landing report within the ACMS/ Reports.

Does anyone have a quick explanation on how a modern FDR measures it's G value? Surely we're not still using mechanical G meters.

The ACMS report is usually of little use in measuring G at touchdown due to previously mentioned low sampling rates (at least 16hz is required to catch peak G I believe?) and ....
G is measured in the sharp end and NOT at the gear where it should be measured - a more reliable G would be obtained from accelerometers in the main gear bay
Fuselage flexing and harmonics
Distance from G measurement to main gear?
Rotation or de-rotation rate at touchdown?
.... and I guess a few other things
A sea of O2 masks hanging out and sundry other debris seems to be pretty reliable still:)

The B767 sensor is in fact in the area of the main landing gear. Not sure about other types though.

On the aircraft in question, the 737 NG, the FDR accelerometer is in the right main gear bay just fwd of the B system hyd reservoir.