SkyDemon Forums

Vertical airspace boundary warning accuracy on flight levels

http://forums.skydemon.aero/Topic33128.aspx

By rlcb - 3/30/2021 10:20:08 PM

I'm struggling to reproduce this in simulator mode (how do I adjust vertical speed?). But today in flight, I got an warning which I swear stated "5500 feet", even though the airspace is bounded by a flight level (FL55+) and charted as such in SkyDemon itself.

The alert message confused me. I thought I was well clear, flying as I was on standard pressure to ensure vertical separation from controlled airspace (I was intending to maintain "FL52" to give 300 feet of tolerance, especially as it was a "rusty first flight back" scenario). Seeing "5500 feet" on the alert, I wondered if I'd made a mistake in understanding the airspace when briefing and it was actually defined by altitude. So I immediately switched to QNH and descended. This wasn't great as there was hilly terrain below, and I'd intended to fly as high as possible to keep my gliding options as open as possible. The QNH was 1026 so "FL53" would have been equivalent to altitude 5551 feet - so just busting the vertical boundary had it been defined by an altitude.

Am I right in my recollection that the alert on the screen said "5500 feet"? Could this be corrected to say FL55 please? The airspace was "Yorkshire CTA" (eg. N5357 W00217).

Secondary question: normally SkyDemon wouldn't have my barometric pressure altitude, so I understand that determining where the vertical boundary actually is is a problem. I say "secondary" because I think the alert on screen could still state it properly, as above. Anyway, I understand why the alert went off, and the inaccuracy in the virtual radar view, even though I was well clear. However, in this case I was using a PilotAware that does report barometric pressure altitude. Could SkyDemon be improved by making use of it in this case? I appreciate it's cabin pressure altitude so there's an inaccuracy there, but that inaccuracy would be far less (I think?) than the inaccuracy I think I experienced today - and for comparison against flight levels, this would be the case the majority of the time.

I was using SkyDemon for iPad 3.15.1.295.
By Rowan - 4/6/2021 3:50:38 PM

 
Tim Dawson - 3/31/2021 9:07:43 AM
You're absolutely right. Internally, SkyDemon is converting everything to altitude to that it can cope with complicated bits of airspace that have two different lower limits depending upon terrain. However for a simple piece like this where the lower boundary is a flight level, the warning would be more helpful if it actually said the flight level, so we will make that change for the next version.

It would be possible for us to use barometric altitude based on a cabin-based pressure sensor in some cases, but there hasn't been much demand for such a feature. It would also be possible for us to look at the nearest QNH and make a better guess at the actual altitude of a FL, but it wouldn't be foolproof and it's not clear whether that would ultimately be helpful or not.


Perhaps use SE2 as the basis for FLs?