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77west
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Limitations On A Heavy Twin Out Of Johannesburg

Tue Nov 12, 2013 2:48 am

Hi all

After reading some stuff about the limits on twins out of JNB, I ran a calculation for a 767-300ER

(I don't have 777 numbers available)

and the results showed that a flight to Europe from JNB would almost not be possible.

As follows: FAOR-EGKK, 22degC with 9kt headwind departing runway 03L, using Flaps 15 and packs off,

I get a field limited MTOW of 154,577kg. With absolutely zero payload, it would only just make the flight.

Pretty much any payload puts it over the field limited MTOW. Fuel came in at 64,800kg. (Seems a bit high?)

How did Nationwide Airlines used to operate to Gatwick with that sort of restriction? 230 passengers would be roughly 23,000kg of payload.

Even if my fuel estimate is 10,000kg to much, that's still only half the possible passenger load.

Also, if anyone had the numbers, what would a 777-300ER's field limited MTOW be in the same conditions?
77West - AW109S Grand - B190 - Q300 - ATR72 - DC9-30 - MD80 - B733 - A320 - B738 - A300-B4 - B773 - B77W
 
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Francoflier
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Wed Nov 13, 2013 7:10 am

Given the same conditions (assuming 1013 hpa / 29.92 hg, which is usually not the case in JNB), I got around 320~322 Tons for a -300ER with packs off and TO bump thrust.

Not sure what a flight to Europe would require fuel-wise. Probably around 70-75 T including alternate and reserve. That would still give, very roughly, around 70T of payload.
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StTim
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Wed Nov 13, 2013 8:49 pm

Delta fly a 777 from JNB to ATL. It is a 17 hour plus flight mostly over water. It leaves early evening in Jo'burg.
 
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seabosdca
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Wed Nov 13, 2013 9:41 pm

Quoting StTim (Reply 2):
Delta fly a 777 from JNB to ATL. It is a 17 hour plus flight mostly over water. It leaves early evening in Jo'burg.

That is a 777-200LR. A 777-300ER would not be able to make that flight without a stop.

Quoting 77west (Thread starter):
I get a field limited MTOW of 154,577kg. With absolutely zero payload, it would only just make the flight.

Your field-limited MTOW seems wrong. Looking at the 767-300ER ACAPS (with high-thrust engines, which any JNB operator would have) it looks to me like on a warm day at JNB's altitude you should be able to lift over 170 t before hitting the tire speed limit. That would be more than enough to get you to LGW.

Edit: Looking more closely I think you need flaps 5, not flaps 15.

[Edited 2013-11-13 13:45:52]
 
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77west
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Thu Nov 14, 2013 1:47 am

I realized I was factoring in an obstacle incorrectly.

After re-doing the calculation, I get:

230 pax + bags = 22,310kg payload. Using an OEW of 90,011kg we get ZFW of 112,321kg.

According to calculations, fuel required is 70,300kg.

This results in a TOW of 182,321kg - within the MTOW of 186,880kg.

However - the system now says that at Flaps 5, Packs and Anti-Ice off, 22degC and 1020 pressure, with 9kt headwind component,
our field limited MTOW is now 171,192kg. This still implies that either my fuel calculations are wrong (probably) or that we
have to leave half the passengers behind, being 11,129kg overweight. 70 tons does seem like a fair bit of fuel for a 767. Flight is 5175nm (nominal).

I was just doing this to see roughly what the performance hit on a twin is from hot and high airports.
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seabosdca
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Thu Nov 14, 2013 2:09 am

Quoting 77west (Reply 4):
our field limited MTOW is now 171,192kg.

That seems just about right.

Quoting 77west (Reply 4):
According to calculations, fuel required is 70,300kg.

That seems very high. I'd expect closer to 60 t, probably on the low side.
 
StTim
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Thu Nov 14, 2013 10:31 am

I am sorry but is a 777-200LR not a heavy twin?
 
Nicoeddf
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RE: Limitations On A Heavy Twin Out Of Johannesburg

Thu Nov 14, 2013 12:11 pm

Quoting StTim (Reply 6):
I am sorry but is a 777-200LR not a heavy twin?

It is - but not one of the two twins the OP was asking for.

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