Keeping the wheels down.....

[Will__]

Just got back from a trip to Africa. We got on a half full plane at Arusha, and flew 50 mins to Dar es Salaam, where half left again, more people got on and then we left to fly 9 hrs 45 mins to Amsterdam. For this flight, the Captain explained that there would be increased noise for the first 10 mins of the flight since they would be leaving the undercarriage down for 10 mins to cool it down. Hmm. Does landing twice with a full plane (Boeing 767 or something) within a couple of hours really need these extreme measures? Surely the brakes would cool down anyway over the next 9 hrs since they're not pressurised in their 'containers' in the underbelly?

Ta.

[Ewood27]

I don't know those airports, but if they're "hot and high" the low air density means the brakes won't lose heat as quickly as normal, and if the landings were on short runways the Captain will have had to use the brakes quite enthusiastically. They may well have been a bit too warm. On the Boeings there is an indication of brake temperature in the cockpit.
Yes, the brakes would cool down nicely on the long flight, but by then the heat might have heat-soaked into the tyres and burst them. Not a good idea! Aircraft tyres have a thermal plug designed to deflate them if the temperature gets too high, but it's better to have inflated tyres to land on. Quieter too!

[Ewood27]

Another possibility - if the aircraft had to taxi a long way at Dar es Salaam, where it would have been heavy with the fuel for the long flight, that alone would build up a lot of heat in the tyres. Certainly leaving the Dunlops dangling for a while is a recognised way of cooling them down.

I remember a badly worded instruction for another aircraft type, that if it was taxied more than five miles in one hour, the wheels must be down for ten minutes in that period. What they meant was that if you are doing flying training, leave the wheels down occasionally, but on first reading it seems you could permissibly taxi most of those five miles with the wheels up!

[Maude]

The problem at Dar is the number of potential stowaways trying all sorts of antics to get into the wheel housings. It is now pretty standard practice to leave the wheels down for 10 or 15 minutes so that they are either blown out or the extreme cold at altitude makes them drop off.

[Will__]

well call me an old cynic but I think that last answer has to be either a joke or an exercise in gullibility. The wheel housings aren't pressurised or heated (afaik) so during a 10 hour flight any stowaways would just freeze or die gasping? (horrible thought but anyway)......

[Maude]

True. But when the wheel housings are opened for landing the bodies drop out which has happened several times already at Heathrow and Schipol. The current thinking is that it is far better to leave the bodies in their country of origin rather than have foreign bodies descending along Hounslow High Street.

[chrislangham]

The northern perimeter road Maude?