What is flight level 90? I'm confused.

[Dragonmount 5]

So I had a flight today from EGLL to LSGG, and along the way on my desecent it asked me to go from what I assumed was fl 12 (12000 ft) to fl 90 (9000 ft) I'm confused because when I got there it kept yelling at me that I had not hit my altitude. I was using the qnh it had set for me by the ATC. It didn't mean go up to 90k ft did it? That would make no sense 8 minutes from the airport.

[19dcavscout 39]

90,000 feet would be FL 900. I am sure it was a mistake of some sort, or the pressure setting they gave you was off of what the pressure setting was outside and you were a few hundred feet off. Also if they are using FL still, you should be at standard (29.92 or 1013)

[Ray Proudfoot 8,954]

As Nick has pointed out when you are instructed to climb or descend to a Flight Level you should be on standard pressure of 29.92" or 1013.2hPa.

 

Simple rule makes it easy to remember. You only switch to QNH when instructed to descend to an altitude such as "five thousand feet".

[Dragonmount 5]

Ah, maybe that was my mistake then.  Thanks for the info!

[bowingic 7]

Not necessarily your mistake about it being  FL90...some transition levels are below 9000 feet...in which case FL90 is correct....so you should have descended to 9000 feet but with standard pressure set as stated above ( rather than the QNH which you set).

The pressure difference between standard and QNH was why you didn't reach the required altitude.

Transition levels are usually shown on STAR charts.