Hello all, I have been using the Fenix EFB T/O performance calculator ever since and most of the time, the calculations seemed to be reasonable. Yesterday, I flew out of Oaxaca Xoxocotlan Intl airport in Mexico (by the way, the scenery by Dreamflight Studios is amazing!), which sits at an elevation of 5000 feet. This place is basically like Denver in the summer, but with one half to one third of the runway length. Before departure, I used the following parameters for my T/O calculation (A320 IAE):

Runway = MMOX 01
TOW = 65543 kg
OAT = +31°C
Wind = (amounted to ~9 kts crosswind)
Flaps = 1
A/C = packs off
 

The EFB returned values of Flex = 55, V1 = 133, VR = V2 = 140. I actually had my doubts about these figures, but I wanted to try them anyways. As I accelerated down the runway, I noticed that I wasn't gaining near enough speed to ensure a safe departure off the runway. For the first time that I can remember, I firewalled the throttles to TOGA, but only managed to become airborne at the very end of the runway (and certainly below 35 feet when passing the threshold). If this had been a real flight, it would have been a near disaster comparable to the recent TUI B738 event at Bristol (see here: https://avherald.com/h?article=5194536c&opt=0).

As part of my own "post flight investigation", I ran the numbers through the new Simbrief calculator, which came up with quite different figures: Flaps 3, TOGA (or Flex = 35 with packs off), V1 = 127, VR = 129, V2 = 132. Flaps 1 wouldn't have even permissible at this take off weight. The stop margin of 155 feet is still pitiful, which makes this take off a very delicate affair.

To me it seems that Fenix EFB will generate numbers at any rate, even if the take off would never be safe nor permissible. Simbrief seems a lot more accurate, even though I haven't tested it yet. Based on this experience I would recommend using the latter, especially in situations where the margins are extremely low.

 

 

 

Thx for sharing! Will give simbrief a try again.

I've had the same finding on a few higher altitude airports with CFM engines, at least ZWSH and OIII. Also slammed TOGA and was able to get clear if with extra excitement. Have to compare with Simbrief next time!

Interesting, I have not tried the SB calculator as of yet but I do find the Fenix EFB gives me Flex temps that are a bit too high most of the time.  I always reduce it by another 5+ degrees....

Edited June 11, 20241 yr by Flic1

I had the same observation at ZULS recently. I checked SimBrief afterwards and those numbers looked a lot more plausible. Remember to open a ticket at Fenix, so they can reproduce and fix the issue.