Hotel is for Helicopter

May 17, 2016 8:21 PM

Does the 'H' commonly seen on helipads indicate to the pilot on what angle he should land?

The 'H' seems to be a kind of natural fit for aligning the helicopter skids to - for instance if the area has prevailing winds from some direction, and the safest angle of approach is a certain angle or whatever. Is this the actual case? Is it a mandated standard or just a platonic ideal where aesthetics might be the deciding factor?

(Asking due to a plan to 'grow' an H in a patch of dry grass in a rural, high air traffic area, as the tiniest of 'jokes'. Should probably ask - that's... safe? right?)

posted by quinndexter to Travel & Transportation (7 answers total)

It seems to me that wind direction (which varies) would be the paramount consideration in landing, so I'd guess not. Only a guess though, no aviator me.
posted by Miko at 8:25 PM on May 17, 2016

Best answer: Your intuition looks to be correct. This FAA document on heliport design states:

(1) Standard heliport identification symbol. Mark the TLOF with a white “H” marking. The “H” has a minimum height of the lesser of 0.3 D or 10 feet (3 m). Locate the “H” in the center of the TLOF and orient it on the axis of the preferred approach/departure path. Place a one-foot wide bar under the “H” when it is necessary to distinguish the preferred approach/departure direction.

If you look at the diagrams in the document, the H is aligned so that the skids of the helicopter would be aligned with its vertical bars.
posted by zsazsa at 8:52 PM on May 17, 2016 [3 favorites]

Best answer: zsazsa has the reference but for helicopters there's a difference between 'approach/departure' direction and landing direction - or there can be. Approach/departure direction is usually based on the prevailing wind but can also take into account obstacles, air traffic considerations, and probably other things I'm not thinking about. Once the helicopter is over the spot it will typically rotate into the wind for landing although skidded helicopters will sometimes land out of the wind to be oriented to airport parking schemes or tiedowns.
posted by macfly at 9:02 PM on May 17, 2016 [3 favorites]

Best answer: Essentially yes, but in Canada they use an aiming point (essentially the apex of a triangle) which is aligned with the magnetic north except in areas of compass unreliability where it shall be oriented with the true north, because otherwise you could face either way on an H. Check out figures 5.1 and 5.4 here.
posted by furtive at 9:05 PM on May 17, 2016 [1 favorite]

Response by poster: Yep, I get that there's a few more factors and pilot discretion in play with any actual landing, but was thinking more as guide I guess for say, pilots unfamiliar with an area. The diagrams linked by zsazsa do show the verticals aligned with designated 'approach/departure' areas mentioned by macfly, which I'd assume would be aligned according to prevailing conditions or preferred approaches. With the 'landing either way' issue, I'd again assume that would be dictated by the approach, and it's implied by 'approach/departure' that either way is prob OK. with maybe lights and windsocks being guides.

Thanks all - the H will go thataway.
posted by quinndexter at 10:24 PM on May 17, 2016

(Asking due to a plan to 'grow' an H in a patch of dry grass in a rural, high air traffic area, as the tiniest of 'jokes'. Should probably ask - that's... safe? right?)

This might be something to double check with the FAA (or relevant legal authority if you're not in the USA), I think.
posted by feckless fecal fear mongering at 10:31 PM on May 17, 2016 [4 favorites]

Response by poster: This might be something to double check with the FAA (or relevant legal authority if you're not in the USA), I think.

The local RAAF base. If they take a slightly greener patch of H-shaped grass seriously, I'll cop it just for the Youtube hits.
posted by quinndexter at 10:46 PM on May 17, 2016 [2 favorites]