GIV questions

[landlover]

Hey! how do most compensate for a gust factor on landing/landing init? Tech manual or FMS book aren't much help. Also does anyone know of a publication that lists all capabilities of AFIS.

 

[K.V.]

I don't think there is a way to add for gust factor in the perf computer. Just add half the gust factor to your ref speed and dialing it up in man speed.

 

[TransMach]

GIV Approach Speeds

The FMS automatically adds 10 knots to ref so that takes care of gusts up to 20 knots. Landing heavy, near 66,000 pounds you'll have a ref speed of 149 and a FMS bug speed of 159 ... your true airspeed will likely be near 175 at that point ... are ya sure you want to add anything more?

TransMach

 

[K.V.]

The FMS automatically adds 10 knots to ref so that takes care of gusts up to 20 knots. Landing heavy, near 66,000 pounds you'll have a ref speed of 149 and a FMS bug speed of 159 ... your true airspeed will likely be near 175 at that point ... are ya sure you want to add anything more?

TransMach

Absolutely. The way I understand it is that ref+10 speed (which is a pre-programed parameter, that can be changed), is your Vapp, the speed at which you're suppose to come down the pipe at. If you hold that speed until 50' over the threshold, chop the power and flare, you should touchdown at ref (any less, and you start to loose elevator affectivity for the flare). If you have a gust factor, you should fly Vapp+ half the gust factor (up to 7 knots; I think I read that somewhere), to 50' over the threshold, chop the power and touchdown at ref+1/2 gust. This way, you're also set up incase you have to go around.

I'm sure, just like many other things in flying, there's a couple different ways to skin this cat. It probably just depends on how you were trained.

I'm certainly open to other thoughts, though.

 

[gern_blanston]

Part 25 landing performance is based on ref and idle at 50 feet, isn't it? Touching down at ref + 1/2 the gust is pushing it, no?

 

[TransMach]

Part 25 landing performance is based on ref and idle at 50 feet, isn't it? Touching down at ref + 1/2 the gust is pushing it, no?

Yes, that is how Part 25 landing distance is derived. If you land a GIV properly (according to GAC) you cancel autothrotles and autopilot so as to arrive at the 50' screen height at Vref at idle thrust. Touch down occurs at Vref -5 with 400FPM vertical veliocity followed by max braking.

The FMS allows selection of auto ground spoilers or none, but flaps 39 is the only flap selection available.

The trick here is that until you have weight on wheels or wheel spin-up, the engines are still at high idle which is 67% HP, a good bit above the scheduled 48% HP ground idle speed. This thrust takes some practice to manage into a landing flare without floating into the next county and another good reason to stop adding more Vapp speed increases. At Vref+10 (automatic) plus a couple more, no more than 5 knots, you have enough kenetic energy to slice through the chop and sheer.

And it's a GREAT cross wind airplane. Much better than the GV.

TransMach