Maynard wrote: ↑Thu Jan 23, 2020 4:16 am
digits_ wrote: ↑Wed Jan 22, 2020 7:51 pm
Maynard wrote: ↑Wed Jan 22, 2020 5:04 pm
-not certified for anti ice fluid De ice fluid can be applied an airborne within minutes on a res
Sounds good, doesn't work (properly).
Timing starts when you start applying. The time you save because you are close to the runway (if you don't need to deice), you lose again because of the, generally, improvised way the plane is sprayed. It is often less efficient than a spray with a proper truck. Type 4 would solve this issue completely. Type 1, sort of works in some situations. If everybody used the type 1 times as hard limits, a whole lot less flights would take off...
If it’s snowing and cold enough, you don’t need to spray. If it’s snowing and warm enough you need to, you have lots of time. If it’s freezing precip, you shouldn’t be there anyways. If it was costing them a large amount cancelling flights because they can’t have a longer HOT, companies would have splurged and paid to get it approved. It’s not worth it for the small amount of days/situations they’d need it.
Lot's of time with type I fluid? Not really...
I found this chart online for type I. It might be off by a couple of minutes, but it gives a good idea.
I'm assuming that most northern operators have something in their COM that says you can only use the lowest value in those charts unless a tactile inspection is performed right before take off. Since the door is right in front of the prop, we'll have to use the lowest value, as a tactile inspection is not possible. Timing starts when the final (only) application of fluid starts, so right when the deice starts.
As a reminder, snowfall intensity is not determined by the metar, but by combination of temperature and visibility.
With these definitions, I've rarely seen very light snow. That leaves 11 minutes in -3 and warmer, or 8 minutes between -6 and -3.
The deicing process would take at least 8 minutes with homebrewed solutions. Even a CDF can take 6 or more minutes. Then you have to start the engines, can easily take another 3 minutes on a metro. 1 minute for an engine start, 1 minute to let the amps come down, 1 minute for the other one. With a GPU you'll save some time for the amps, but you'll lose it again because the GPU has to be disconnected. So you'll be right at the 11 minute mark before you even start moving. Time to shut down and spray again...
What happens in reality? Pilots look outside, judge the wing is ok, and leave. They are breaking procedures. Is it unsafe? You can debate that. In lots of conditions the holdovertimes are pretty generous. If pilot would stick to their company procedures to the letter, way more flights would get cancelled.
This is not just aimed at perimeter by the way, pretty sure the majority of northern operators runs into issues like this. But if we compare this to the king air, you can (and it happens) walk outside right before line up, because the door is behind the engines, and do the actual inspection which gives you extra time.