Some more tricky questions

[Speedwinner]

Hey folks,


appreciating a lot of inputs ! Thanks!


1. Doing a circling approach and on very short final you have to do a go around. What climb gradient do i have to make when i fly the opposite ils or approach sector up to the msa? Any restrictions single engine? Somebody told me 5,5% but didnt know where he got this value from




2. Old discussion: but does the cwc have a real big effect on the vmcg? Example B 737 wet runway and v1 is equal to vmcg. Boeing says that there are enough margins calculated. Is that true? what about 25kts tailwind which is limit at out airline company?



3.Holding with the 737. Programmed and prior entering the hold the FMS message "Unable hold airspace" appears. Any explanation on that?




4.Flying an non-precision approach. How can i calculate the visibility i need to have to see the runway? Any nice and easy formulars?


5. old discussion. The MAP. For example we fly an approach into a field and the missed approach point is at the runway. the missed approach goes straight ahead till 5000 and 10dme from the field dme. dont understand that one. is it relevant? also for ILS approaches?

Thanks folks!


SW

[Mad (Flt) Scientist]

2. Old discussion: but does the cwc have a real big effect on the vmcg? Example B 737 wet runway and v1 is equal to vmcg. Boeing says that there are enough margins calculated. Is that true? what about 25kts tailwind which is limit at out airline company?

Depends somewhat on aircraft, but Vmcg at test conditions may have a sensitivity in excess of 1knot VMCG per 1 knot Xwind. So a typical max demonstrated type Xwind of the order of 30 knots will increase the 'real' Vmcg by the same kind of magnitude.

Boeing are slightly talking out of the side of their mouth - but then so is everyone else when asked the same question. The reality is that a large enough xwind component with a critical engine failure and other factors against you (such as cg and runway state) will VERY quickly have you off the side of the runway. Pretty much true for every transport category aircraft - they all meet pretty much the same rules (VMCG demonstrated in calm conditions, NWS off, aft cg) so they all have pretty much the same margins.

The regulators (not the OEMs, it's ultimately a regulatory decision) accept this state of affairs as an acceptable risk, given the inherent unlikelihood of that bad day happening, and the massive operational impact of trying to provide absolutely safety (something that can't be attained anyway).

Any tailwind effect will be far less marked - the Vmcg is basically an airspeed, so at the same airspeed you'd have a higher groundspeed, so MIGHT get a propritionally larger deviation since the aircraft-to-runway relationship depends somewhat on speed over the ground. (This might also imply that Vmcg should be a function of altitude, all other things being equal). But I doubt it's anything like as powerful as xwind.

[Intruder]

1. Do you know what climb gradient your airplane has in any particular configuration? If you don't, does it matter?

4. 300 ft/mile is a normal descent profile. If you do a constant descent profile to your minimum descent altitude, to reach it at the Visual Descent Point, that is about the distance you will be from the runway.

[c100driver]

1. Doing a circling approach and on very short final you have to do a go around. What climb gradient do i have to make when i fly the opposite ils or approach sector up to the msa? Any restrictions single engine? Somebody told me 5,5% but didnt know where he got this value from

Off a circling approach you fly the missed approach for the approach you have just flown, so I fail to understand why you would want to work out a gradient for something that you would not do? While you would probably be safe flying the missed approach procedure for the opposite runway, you would be making it up "on the fly", so would not be flying a published procedure i.e. you are on your own!


3.Holding with the 737. Programmed and prior entering the hold the FMS message "Unable hold airspace" appears. Any explanation on that?


It usually comes up with "UNABLE HOLD AIRSPACE" because the aircraft is too fast for the hold to be flown with the LNAV aob limits.