High altitude cold weather corrections

[AuxBatOn]

What was the temperatures and altimeters settings at the enroute airports? This isnone thing I check on my pre-flight.

If ATC tells me the min safe is X, their altitudes are temperature adjusted so I'll go with that.

For the second one, I'd need more information from my flight planning.

[pelmet]

What was the temperatures and altimeters settings at the enroute airports? This isnone thing I check on my pre-flight.

If ATC tells me the min safe is X, their altitudes are temperature adjusted so I'll go with that.

For the second one, I'd need more information from my flight planning.

Vancouver is 0C and 29.52, Edmonton is -30 and 30.09. Anchorage is +5 and 29.47 while Fort St. John was -25 and 30.30. For some reason, you can't remember the Whitehorse weather as you had some other issues to deal with before departure and enroute.

ATC did give you an Min safe altitude which gave you comfort but your copilot was finally able to adjust his mask and say clearly enough to remind you that ATC only temperature corrects vector altitudes, at least he thinks that is the case. Do you want him to look it up in the AIM?

And, as suggested earlier, your portable WAAS GPS is somewhere in your flightbag and ACARS is still working if you want to access the latest metars. But you only have about 20 seconds left now to get to the published MEA, or maybe it is a bit more. There seems to be some increased turbulence, possibly mechanical turbulence in the blackness.

[AuxBatOn]

For the second problem:

The worst case is:

500 ft for altimeter setting error (10 ft per 0.01 in Hg below 29.92)
I can't remember Fort St John's altitude so I'll take worst case, sea level so that's ISA-40 and a 20,000 ft obstacle. 20*40*4 = 3,200 ft

Total error around 3,500 ft (knowing I am being conservative) so I'll initially descend to 23,500 ft until I can figure out where I am and how much lower I can descend

[AuxBatOn]

ATC did give you an Min safe altitude which gave you comfort but your copilot was able to say clearly enough to remind you that ATC only temperature corrects vector altitudes, at least he thnks that is the case. Do you want him to look it up in the AIM?

They'll give you a min vectoring altitude which should be below MEA.

[pelmet]

ATC did give you an Min safe altitude which gave you comfort but your copilot was able to say clearly enough to remind you that ATC only temperature corrects vector altitudes, at least he thnks that is the case. Do you want him to look it up in the AIM?

They'll give you a min vectoring altitude which should be below MEA.

You can hear Edmonton center talk to you at your level off altitude when you push the squelch button. Through the static, they advise that radar contact is lost from their enroute radar and wonder if you have ADS reporting capability. They also say that should be able contact Anchorage at 141W.

They say from your estimated position that there are lower obstacle clearance altitudes in all directions with the ocean about 100 miles to your left, published 15.5 altitude 80 miles ahead or so, 16.5 about 80 behind you and 19.8 about 80 miles to the right. They want to know your intentions. Fuel was a bit below flight plan burn for your planned destination at Anchorage at near max landing weight with Elmendorf as the alternate(7 miles away) so it looks like Vancouver will be a stretch as you really do want at least 8000 feet of runway.

There has been no contact from the flight attendants because you did'nt give them any signal due to your altitude but your aircraft does have 22 minutes of oxygen capability which hopefully will be satisfactory for the old ladies on board.

[AuxBatOn]

Continue ahead towards destination at 23,500 ft for 80 nm. Squawk 7700. Assuming at least 4 nm/min groundspeed (240 kts gs), this will take less than 20 minutes. However, I would set the max power setting that would get me there with enough fuel (forget IFR reserves), planned for 15,000 ft. If the weather is forecasted 1,000 ft AGL/2SM or greater, right down to 10 mins of fuel left. If below that, but above minima, add an extra approach. If below minima, add a transit to alternate. In the mean time, break out enroute charts and figure out the best way to get there while minimizig altitude. Below 18,000 ft, I could deal with but ideally, I want to be below 15,000 ft.

[pelmet]

Continue ahead towards destination at 23,500 ft for 80 nm. Squawk 7700. Assuming at least 4 nm/min groundspeed (240 kts gs), this will take less than 20 minutes. However, I would set the max power setting that would get me there with enough fuel (forget IFR reserves), planned for 15,000 ft. If the weather is forecasted 1,000 ft AGL/2SM or greater, right down to 10 mins of fuel left. If below that, but above minima, add an extra approach. If below minima, add a transit to alternate. In the mean time, break out enroute charts and figure out the best way to get there while minimizig altitude. Below 18,000 ft, I could deal with but ideally, I want to be below 15,000 ft.

Thanks...

I see that you changed your reply. Before, you had a formula that you used to get the 23,500 foot altitude. Could you post it again as I wanted to try it at other altitudes.

[digits_]

Continue ahead towards destination at 23,500 ft for 80 nm. Squawk 7700. Assuming at least 4 nm/min groundspeed (240 kts gs), this will take less than 20 minutes. However, I would set the max power setting that would get me there with enough fuel (forget IFR reserves), planned for 15,000 ft. If the weather is forecasted 1,000 ft AGL/2SM or greater, right down to 10 mins of fuel left. If below that, but above minima, add an extra approach. If below minima, add a transit to alternate. In the mean time, break out enroute charts and figure out the best way to get there while minimizig altitude. Below 18,000 ft, I could deal with but ideally, I want to be below 15,000 ft.

Do you trust your fuel gauges enough to be accurate down to 10min ?

[AuxBatOn]

In a modern aircraft, knowing what the unusable fuel and gauge accuracy is, absolutely, especially since this would be conservative in many sense.

[pelmet]

Continue ahead towards destination at 23,500 ft for 80 nm. Squawk 7700. Assuming at least 4 nm/min groundspeed (240 kts gs), this will take less than 20 minutes. However, I would set the max power setting that would get me there with enough fuel (forget IFR reserves), planned for 15,000 ft. If the weather is forecasted 1,000 ft AGL/2SM or greater, right down to 10 mins of fuel left. If below that, but above minima, add an extra approach. If below minima, add a transit to alternate. In the mean time, break out enroute charts and figure out the best way to get there while minimizig altitude. Below 18,000 ft, I could deal with but ideally, I want to be below 15,000 ft.

Thanks...

I see that you changed your reply. Before, you had a formula that you used to get the 23,500 foot altitude. Could you post it again as I wanted to try it at other altitudes.

[BGH]

Sorry about this post,tried to delete it but it won't let me.

I was taught that cold weather corrections were done on departure approach & arrival;atc corrected enroute altitudes.I f you corrected your altitude you were supposed to let atc know what the correction was.
In uncontrolled airspace you corrected altitude & then used the next higher altitude for direction of flight.
Seemed easy enough.

Daryl

[JeppsOnFire]

Sounds like a SIM instructor taking out his bad day on you. Extreme cold weather on the earth's surface will not continue in a standard lapse rate to the flight levels. Likely it would be -65 for a few thousand feet, then warming for a while, then cooling again to some reasonable-ish levels up high. ** I'll add that this has been my personal experience flying in very cold weather and also at very high altitudes all over the world. Someone will probably come up with some formula saying otherwise because this is Avcanada.

You don't often fly over terrain that high, so when you do, you're very much aware of it. This is what I would do in that extremely unlikely scenario. (pelmet says: The time for formulas, correction tables and lapse rate discussion is over.) Sooo:

Descend to FL250. If for some reason there is a problem with the O2 masks and I need to get lower right now and I can't talk to ATC or the FO and I'm really really scared, I'd probably just keep looking at my TAWS display on the MFD and keep all the pixels green.
If fuel is a problem, I'd just go to the airport I calculated (when I say 'I' of course I mean the internets calculated for me) for just this scenario (depress, medical emerg, OEI diversion airports).

At no time during this process would I consider pulling out my scientific calculator or the bloody AIM.