Flying over a typhoon

[The Mongoose]

I'm preparing for my second interview and I can't find the answer to a question that I recently came across. How does temperature change when flying over a tyhoon and what concerns would you have flying over the top of a typhoon?

Thanks for your help.

[404 Titan]

The Mongoose

The temperature rises, sometimes quite markedly. This results in a reduction of engine and aerodynamic performance and the possibility of ending up in coffin corner. Remedy is to descend to a lower altitude before you cross the typhoon/hurricane/cyclone so you have the performance up your sleave when the temperature rises.

[The Mongoose]

Thanks Titan

[404 Titan]

DirectAnywhere

I here what you are saying. Unfortunately in this part of the world that can sometimes be very hard to achieve because of some of the political issues and the nature of a lot of the airspace. Countries with very inflexible ATC systems and crowded airspace.

[7FF]

Both the above answers are correct. ISA deviations of +25 are not uncommon. Typhoons tend to be low level affairs apart from the towering CB's.

[FlexibleResponse]

Titan is correct,

In areas of typhoon, plan to fly at least 4000' below the max performance cruising altitude that the chart temps show you. The localised areas of high temperature around typhoons are not accurately depicted in meteorologist charts.

[TAC inop.]

This one intrigues me just a little....so you are saying that an increase in temp will bring the low and high boundries closer together?

The thing is, that if you are not cruise thrust limited ... at optimum FL, low cost index ....then there would be little to worry about in the thrust department even with a temp increase.

[Cedar Tree]

Thanks for the explanation guys, it makes a lot more sense now! What about drift-down performance, with the 330 going to NZ/OZ it must be a huge factor with the increase in temps?

[TAC inop.]

Don’t be too worried about this ‘Increasing temps’ thing CT.

Driftdown One engine inop .. if you are cruising at your FMC optimum FL, you’ll fall about 10,000’ in a B777.
Take off an extra 1000’ for every 5 deg ISA deviation above +10 for a -300ER, and an extra 2000’ for the same deviation for a -200ER

So, just back to the typhoon thing. I don’t know about Airbus, but the B-777 200 ER is thrust limited at mid-ish cruise weights about 3500’ above optimum in ISA to +10 and 2000’ above opt ISA + 20.
The 777-300ER is not Thrust Limited but is limited to Manoeuvre Margin, weight/FL only.
I plucked these figures out of the QRH for LRC ( low-ish Cost index, around 140 ). Remember that the FMC will recommend Optimum based on wind, weight, temp, and Cost Index, and compute it for the coming 500 nm.

. It’s one of those funny interview questions that is made up to examine knowledge on a couple of subjects, but isn’t all that practicle.
Firstly, don’t overfly the thing! The flight planning fellows have probably taken care of this for you anyway, afterall, its a plotted, tracked, large WX phenomena that didn’t just appear overnight! Driftdown strategies and alternates would be a nightmare. Its not like a few CBs in the Bay of Bengal, which are nasty enough to route around, we’re talking about the known position of a large and nasty tropical WX system.
Ok, then let’s say you have to fly over it for god knows what reason.
You are awhere that there will be an OAT increase as you approach the centre, fine. You’d examine your Max Alt margin on the cruise page of the CDU. Now, in a 300ER it doesn’t mean a hell of a lot, because it’s not a thrust limited FL, but in a 200ER it is, and any increase in temp will lower the Max FL. So, you are cruising at FL 340, and your Max is FL376. It’ll take a BIG temp increase to make your day worse than it already is. Even +20 wont really worry you.
You need to know what will happen, why, and how to ascertain that you have a safety margin for your aircraft if you need to do this sort of thing………. and you also need to be awhere that you wont get laid that night in the hotel, because the girls in the back will be really pissed you.

Cheers
TAC

[TAC inop.]

Yeah...very interesting indeed
Can you enter a temp in the CDU cruise page to check limits?

[FlexibleResponse]

If I might emphasise DirectAnywhere's very good advice, let me say:

Max recommended cruise altitude depends on only two factors:
1. Weight; and
2. Temp (determines thrust).

As you know, your checklist or QRH (Quick Reference Handbook) will have charts or tables to determine max cruise altitude based on the above two variables.

However, approaching an area of Cyclonic or Typhoon activity the temp will rise rapidly. It is recommended that you add about 8-10 deg to the current temp or reduce the recommended max cruise alt by 4000' to determine what cruise alt to transit the area.

Your MCDU prediction of max cruise alt will be based on current temps or met forecast entered temps. The met forecast temps are not accurate in areas around cyclones or typhoons. When you get into the actual high temp areas your MCDU will tell you the truth but unless you have allowed for that, it will be too late.