Lowest DA?

Matthew

Matthew

Touchdown! Greaser!
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Matthew
This afternoon was a cold, clear day. 30.38 on the altimeter and the density altitude was broadcast as -1600'. Field elevation is 1087', for a total difference of 2687'.

I think -1600' is a new record for me.
 
Current DA at UGN is -3457.

30.32 altimeter
-18.1c
728 field elevation.

It's cold, and shrinkage is in full effect.
 
That’s not very low. I routinely see -2500. It’s -2900 over most the Midwest tonight.
 
Normally I'm used to seeing high DA since I do way more flights in the summer. -1600 is pretty low for me.
 
I think the lowest I've seen was -4400, at a field at 1310' (and yes, I still know the exact elevation of my training field. :p ). The lowest I've flown was in the -3000s.
 
A few times in Alaska, field elevation 30 feet, temperature was above -38f, DA reading was -6000. -4000 DA was pretty normal in winter.

The planes I was flying had a tremendous rate of climb even fully loaded.
 
In Chicagoland, I did my primary flight training in weather that was -2000 to -4000 DA. There were days where we couldn’t get a power off stall to the break in a 172. It also made power on stalls very intimidating as the deck angle had to be quite high!
 
Love flying in low DA. Plane climbs like a homesick angel.
 
Caution:
This was eye opening for me, I was cruising at 9500' and GPS altitude was 8800" or so with an OAT of 0F. I found that noteworthy but put it in the back of my brain. As my destination, started an approach, 2500' IAF, OAT 8F, 30.39 in Hg. As soon as the GPS went into approach mode, it alerted that I was too low, at 2150 ft or so. Wisconsin is plenty flat and I could see out the window fine so no risk of CFIT, but that nudged me to dig in a bit more.

Approach plates will have the snowflake symbol and instructions as appropriate but there is also an ICAO cold temperature error table. This is something you can negotiate with ATC to give yourself back some safety margin.
https://www.faa.gov/air_traffic/publications/atpubs/aip_html/part2_enr_section_1.8.html
 
The other night it was-1750 with a field elevation of 600’. Pretty normal around here and yes the plane performs great. It is the only thing I look forward to during winter flying.
 
Zeldman said:
A few times in Alaska, field elevation 30 feet, temperature was above -38f, DA reading was -6000. -4000 DA was pretty normal in winter.

The planes I was flying had a tremendous rate of climb even fully loaded.
Click to expand...

Is it now standard practice to take off with reduced power/manifold pressure when the DA is that Low?

I recall some operators back in the 70's were having issues with broken crankshafts after repeated full power takeoffs at that low of density altitude. Does it work the other way, the rule of thumb is 3% power loss for 1000 feet. So taking off with -6000 DA full power would produce 136% power?

Brian
 
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