Johannesburg Airport take off

[Scrutton Street]

I have recently returned from South Africa and noticed that the take off run from Johannesburg Airport appeared to take significantly longer than usual. I assume this is because the airport is at an altitude of several thousand feet.

Could someone please tell me a) whether this is correct, b) how much longer a similar plane carrying a similar payload over a similar distance would require at Johannesburg compared with, say, London, and c) How much faster we would be travelling at take off.

Many thanks in advance

[The Flying Pram]

Yes, your observation is correct. As the altitude increases the air becomes thinner. This means the wings need to be traveling faster to generate the same amount of lift. The engines will not produce as much power, so the distance to accelerate to this higher speed will also increase. There are numerous cases of lower powered aircraft failing to become airborne even on very long runways. High ambient temperatures will further exacerbate this problem. Pilots should always do performance calculations before attempting to take off whatever the situation.

[Juliet Sierra Papa]

Scrutton Street (http://www.pprune.org/forums/member.php?u=188260) .

You are absolutely correct, the alt here is +/- 6000ft and generally the air is very thin. The temp recently has been pushing 30 C (+/- 86F ?) and also well into the night. I'm not qualified to tell you accurately what V1 and V2 speeds are for given types and payloads/Wx etc but I'm sure that if you could let us know what a/c type you were in and assuming non stop LHR flight someone here could enlighten you further.

Can tell you for a fact that I once Dep Jhb with a 1min 45sec takeoff roll, was nipping a bit during that one.:uhoh:

[Scrutton Street]

Many thanks for taking the time to reply. Actually it was an A330-300 bound for Doha, pretty full, flight time eight hours, just after noon too, so pretty warm. But yes, I have also done it in a 747-400 bound for London and noticed the extra time, so I would be interested in how much longer/faster it would be for either.

The last time I took off from here long haul the crew actually mentioned that the takeoff roll would be longer than normal, but not this time. Certainly felt like an age before we got up, and my wife looked paler than normal as we kept getting faster, but I presume the runway is a bit longer to compensate, or more power is used at takeoff?

1'45"! If I was a passenger I would assume the pilot had decided to drive all the way, not fly.

Once again, thanks for the replies.

[skiesfull]

JNB-LHR in a full 747-400 at high ambient temp requires the curvature of the Earth! Rotate speed at Flaps 20 around 173 knots.

[arem]

JNB 03L length 4400m - on a 744 it would take at least 3500m to get to rotate, but in a 747-200 at max weight we were well into the red/ambers before rotate came up!! - exciting!!

[Juliet Sierra Papa]

Hi Scrutton Street,

Only just seen your reply, couldn't get logged on for a couple of days (server too busy) guess this was the LHR incident. Anyway you're welcome.

Hi arem,

understand what you say about the 742 but I was on 744 and very worried.

[springbok449]

Took off last night in a 340-6 and V1 133 and VR 167 at 352T.
We always make a quick PA to advise the pax of long TO run....

Engine Failure after bird strike in a 747-2 few years ago proved v interesting.

[Midland 331]

NBO is similar. 1.35 in a 747-236 ("Moody's Glider"!) circa 1990. Golly-gosh! It seemed like an age.

r

[Scrutton Street]

Would anyone kmow how do those speeds, distances and times for takeoff compare to the same flight at sea level? ie what would be the difference going from Johannesburg to London, and then bringing the same plane with the same load back from London to Johannesburg?