Qlink Cobham 717s payload limited
Join Date: Jun 1999
Location: Australasia
Posts: 362
Likes: 0
Received 0 Likes
on
0 Posts
critical temps for CBR
Hey Clarrie,
What are the critical OATs for departure 35 for the A and C engines?
A rough look at the BoM max temps for the last 5 years for CBR airport for January shows a monthly mean of 30.3C with a standard deviation of 4.7C, based on 153 daily observations showing a range of max OAT of 23.4C, the highest being 42.0C. The distribution is a reasonably symmetrical approximation of the normal distribution, so even Alan's mathematical genii in Route Planning can easily calculate the probability of a particular temperature occurring during that month. For a slightly bigger bonus, they could probably develop a correlation estimate between the new airport data and the old airport data (kept from 1939 to 2010) and work it out on a daily basis to match the traffic data.
For a huge bonus, they could even talk to Yield about providing a daily seat limit, making it easier for the boys to manage the variations on the day.
Now, getting back to the troll's original bait, the cost of power by the hour for a 21K engine compared to an 18.5K engine is eye-wateringly disproportionate for the number of take-offs required above 18.5K. Let's just say you need 21K for 30 departures but the rest (say 120) are at maximum derate of around 15-16K: you pay for every minute of time in service as if you are spinning the fan off the front at max TGT through the emergency gate.
Would I assess the probabilities of getting away with 18.5K engines
or would I just pay through the nose for 21K and look at it after 3 months? 
Farm Gate,
Anybody limiting TOW to maintain OEI SID compliance at CBR either had big expensive engines or doesn't grasp the benefits of Special Departure Procedures...
Neville N,
I didn't realise that IATA had taken over from the ACCC in protecting consumers...
Stay Alive,
What are the critical OATs for departure 35 for the A and C engines?
A rough look at the BoM max temps for the last 5 years for CBR airport for January shows a monthly mean of 30.3C with a standard deviation of 4.7C, based on 153 daily observations showing a range of max OAT of 23.4C, the highest being 42.0C. The distribution is a reasonably symmetrical approximation of the normal distribution, so even Alan's mathematical genii in Route Planning can easily calculate the probability of a particular temperature occurring during that month. For a slightly bigger bonus, they could probably develop a correlation estimate between the new airport data and the old airport data (kept from 1939 to 2010) and work it out on a daily basis to match the traffic data.
For a huge bonus, they could even talk to Yield about providing a daily seat limit, making it easier for the boys to manage the variations on the day.
Now, getting back to the troll's original bait, the cost of power by the hour for a 21K engine compared to an 18.5K engine is eye-wateringly disproportionate for the number of take-offs required above 18.5K. Let's just say you need 21K for 30 departures but the rest (say 120) are at maximum derate of around 15-16K: you pay for every minute of time in service as if you are spinning the fan off the front at max TGT through the emergency gate.
Would I assess the probabilities of getting away with 18.5K engines
or would I just pay through the nose for 21K and look at it after 3 months? Farm Gate,
Anybody limiting TOW to maintain OEI SID compliance at CBR either had big expensive engines or doesn't grasp the benefits of Special Departure Procedures...
Neville N,
I didn't realise that IATA had taken over from the ACCC in protecting consumers...
Stay Alive,
SIDS N STARS, welcome to the wind up 
Sorry to hear our newly re-fitted interior has been destroyed already.
Regarding the IFE, I am assuming you were travelling between SYD-CBR. How would mainline or the real q-link handle the IFE on a 25 minute sector?
Some one also mentioned the temperatures QF used to predict the performance of the 717. I am told the figures used were yearly mean temperatures (mean max in the hottest month of January 28.5 deg). Which would indicate to the QF performance guys that there would be no restrictions even with 18.5k engines. Obviously an overly simplistic approach you could say.
Sorry to hear our newly re-fitted interior has been destroyed already.
Regarding the IFE, I am assuming you were travelling between SYD-CBR. How would mainline or the real q-link handle the IFE on a 25 minute sector?
Some one also mentioned the temperatures QF used to predict the performance of the 717. I am told the figures used were yearly mean temperatures (mean max in the hottest month of January 28.5 deg). Which would indicate to the QF performance guys that there would be no restrictions even with 18.5k engines. Obviously an overly simplistic approach you could say.
Join Date: Mar 2011
Location: Florence
Age: 74
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
I love it when it gets technical
I am told the figures used were yearly mean temperatures (mean max in the hottest month of January 28.5 deg). Which would indicate to the QF performance guys that there would be no restrictions even with 18.5k engines.
Join Date: Jul 2011
Location: FG central
Age: 53
Posts: 140
Likes: 0
Received 0 Likes
on
0 Posts
Any IFE on a 717 has got to be better than on Qantas's ancient 737's. Nothing like 3 or 4 tiny old CRT tubes (with obligatory safety tape on the bottom for anyone over 165cm tall) and a VCR for the latest and greatest.
How Qantas get away with charging at all for flying in a -200, I don't understand. It's like sitting in a doctor's surgery in 1980....
How Qantas get away with charging at all for flying in a -200, I don't understand. It's like sitting in a doctor's surgery in 1980....
-200's your on drugs. Haven't even had 300's for years. The IFE in the 400's is crap but what do you expect when they will be gone soon.
As for performance issues not alone in that department. QF 737s had issues with de rated 800s going into places.
Why is QF performance doing things for Cobham?
As for performance issues not alone in that department. QF 737s had issues with de rated 800s going into places.
Which would indicate to the QF performance guys that there would be no restrictions even with 18.5k engines.
Does not utilising the offset Type-A chart for RWY 35 (353 degrees) provide an OCTG of around 3.4%? Please note, I'm not privy to the Cobham SOPs, but can they not employ such methods to calculate departure, or is the 717 performance worse than that... From memory (and it's scratchy), the use of the offset Type-A chart permitted departures on RWY 35 ahead of RWY 17 due to the reduced gradient and the lower MSA to the north (4600' vs 5100'/7500' to the south).
Interested to know if I'm a) wrong or b)how they are specifically restricted by a 35 departure.
Thanks.
Joe Lighty
"Nobody's died from pressing..."
Interested to know if I'm a) wrong or b)how they are specifically restricted by a 35 departure.
Thanks.
Joe Lighty
"Nobody's died from pressing..."
Join Date: Nov 2002
Location: brisbane
Posts: 38
Likes: 0
Received 0 Likes
on
0 Posts
It won't matter soon... Once Network get their 20 red tail A320's I don't think the 717 or cobham will be needed much longer (Qf shorthaul either for that matter). Checkmate.
Which would indicate to the QF performance guys that there would be no restrictions even with 18.5k engines.
Originally Posted by Joseph
Does not utilising the offset Type-A chart for RWY 35 (353 degrees) provide an OCTG of around 3.4%?
"It won't matter soon... Once Network get their 20 red tail A320's I don't think the 717 or cobham will be needed much longer (Qf shorthaul either for that matter). Checkmate."
Haha, probably right! They are in the business of going broke
Haha, probably right! They are in the business of going broke
No. Have a look at the current Radar and RNAV SID and tell us what the gradient is.
Options (in order of ease/preference):
1) If you can achieve 6.6% to 3400' - great, easy.
2) Can't make 6.6% - what's the standard (straight ahead - as published in the RDS in ERSA) splay gradient? Can I achieve that? Can I also achieve the 25nm MSA by the end of the splay?
3) Can I use the 5 degree offset splay gradient (I think about 3.4% from YSCB RWY 35 Type A-Chart). Can I achieve that? Can I also achieve the 25nm MSA by the end of that splay?
Surely Cobham/Qantas/Virgin don't always have to achieve the 6.6% gradient requirement?
Last edited by josephfeatherweight; 4th Jan 2014 at 02:12.
Originally Posted by Joseph
3) Can I use the 5 degree offset splay gradient (I think about 3.4%). Can I achieve that?
Join Date: Apr 2004
Location: Australia
Posts: 38
Likes: 0
Received 0 Likes
on
0 Posts
Am I missing something? Generally it is hot weather that causes this issue. Therefore it is probably cavok. What would stop a visual departure being requested? Just a thought, I am no doubt wrong.
How'd you work out 3.4% when the published departures on the 353 (5° rght offset) give a gradient of 6.6%? What splay dimensions are you using?
Originally Posted by Mustang
Therefore it is probably cavok. What would stop a visual departure being requested? Just a thought, I am no doubt wrong.
using the YSCB Type-A Charts
HC RPT DEP at Willy are given a visual dep unless the weather requires a SID or Radar DEP
Ok - a few things to clear up.
The gradient is important to consider in the one-engine inoperative case - it doesn't matter if you're IMC or visual - the only difference is, if you're visual and you're not achieving the minimum gradient to avoid the ground, you'll get a great view of the it before you smack into it...
Type A charts are usually provided by the airport authority and cost a fair bit to a) produce and b) purchase. They identify ALL obstacles in the splay (based off the centreline, usually, but sometimes in special cases they do offset calcs such as at YSCB RWY 35) which is a straight line extending out to 15,000m with a 15 degree "splay" either side. The benefit of a Type A chart over the basic RDS info is that you can identify the most limiting obstacle and hence the most limiting gradient. Pretty sure the splay is based off 35' from the DER - haven't looked for a while and don't have my docs with me...
Anyway, with the above data, you can calculate less restrictive engine out climb gradient requirements...
The gradient is important to consider in the one-engine inoperative case - it doesn't matter if you're IMC or visual - the only difference is, if you're visual and you're not achieving the minimum gradient to avoid the ground, you'll get a great view of the it before you smack into it...
Type A charts are usually provided by the airport authority and cost a fair bit to a) produce and b) purchase. They identify ALL obstacles in the splay (based off the centreline, usually, but sometimes in special cases they do offset calcs such as at YSCB RWY 35) which is a straight line extending out to 15,000m with a 15 degree "splay" either side. The benefit of a Type A chart over the basic RDS info is that you can identify the most limiting obstacle and hence the most limiting gradient. Pretty sure the splay is based off 35' from the DER - haven't looked for a while and don't have my docs with me...
Anyway, with the above data, you can calculate less restrictive engine out climb gradient requirements...