View Full Version : Getting landing G from the FMC
captdini737
28th Mar 2007, 17:00
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.
ahramin
28th Mar 2007, 17:38
Sorry but what is landing G?
captdini737
28th Mar 2007, 17:50
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.
FCS Explorer
28th Mar 2007, 18:09
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....
captdini737
28th Mar 2007, 18:25
Hey FCS Explorer, thanks a lot. Will give it a shot. Much appreciated.
spongebob
28th Mar 2007, 21:30
can pilots access this info? and for how many cycles previous does the info appear for?
cheers
Mad (Flt) Scientist
29th Mar 2007, 01:24
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.
belowMDA
29th Mar 2007, 07:39
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
Mad (Flt) Scientist
29th Mar 2007, 10:14
@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.
Golden Rivet
29th Mar 2007, 10:31
You can get a full landing report within the ACMS/ Reports.
hawk37
29th Mar 2007, 10:54
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.
Golden Rivet
29th Mar 2007, 13:22
G is measured in the sharp end and NOT at the gear where it should be measured
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.