Peter wrote:
This thread is about lowest OAT seen
This was todays Ogimet, has anyone seen the tropopause so low ?
@arj1 wrote:
How did you get to FL250 in an uncertified? Or were you flying IFR?
Simple answer: I got a clearance 
COMMISSION REGULATION (EC) No 730/2006 of 11 May 2006 on airspace classification and access of flights operated under visual flight rules above flight level 195
Article 4 (Access of VFR flights above flight level 195):
In airspace above flight level 195 Member States may establish an airspace reservation, where practical, in which VFR flights may be allowed.
In airspace above flight level 195, up to and including flight level 285, VFR flights may also be authorised by the responsible air traffic services unit in accordance with the authorisation procedures established and published by Member States in the relevant aeronautical information publication.
UdoR wrote:
Dan wrote: notwithstanding the general opinion of this respectable forumI don’t think arj1 was pointing to this, it’s just that max allowable VFR cruising level should be FL195.
SERA.5005 (d) (2). However exceptions exist.
Yes, that was the question. So you’ve raised an exception? Got it.
arj1 wrote:
How did you get to FL250 in an uncertified?
my take is good aerodynamics and a strong engine.
IFR vs VFR regime, or as a matter of fact certified vs non-, doesn’t have an effect on aircraft performance, notwithstanding the general opinion of this respectable forum
europaxs wrote:
-30°C @FL250
How did you get to FL250 in an uncertified? Or were you flying IFR?
-30°C @FL250
This is my personal record last January just off the coast of French Provence
IN case someone interested the actual formula is 99.99% an isentropic flow as described herein by NASA:
Hence it is exactly quadratic with TAS, M and even IAS.
Since density also affects it one could be tempted to use IAS instead of TAS for the calculation of the effect, but then it is also affected inversely by pressure (altitude) for a given IAS , or absolute temperature for a given TAS.
The only way to kind of isolate speed from atmospheric conditions (altitude and temp) is to use Mach no and then it is exactly, in absolute temp the simple formula:
Tt/T= 1+ 0.2 M^2
You can play with numbers in the NASA webpage and you will see that due to temp change in ISA as you climb, temp rise for a given TAS is very similar at all ISA altitudes or 1.4 deg C at 100KTAS or 5.6C at 200KTAS and 12.6C at 300KTAS and so on…
