Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Posted (9 years 1 week 9 hours ago) and read 5978 times:
Hi guys.
A few days ago I was listening to the Toronto Center controller for "high altitude" flights on frequency 134.575.
I was watching the contrails of a 4 engined airliner approaching the Toronto VOR at YYZ from the west when I heard one of it's pilots check in with Toronto Center. They were a Lufthansa flight and were level at FL 330.
The ATC controller advised the pilot that he was radar identified at 33,000 feet and instructed him to fly direct to the MIILS waypoint (in New Brunswick).
The pilot acknowledged ATC's instructions. A few minutes later he flew directly overhead of me and I could clearly see with my binoculars that it was a Lufthansa A340.
Then the controller asked the Lufthansa pilot if he could climb to FL 350 for traffic purposes.
The pilot replied that he couldn't climb from FL 330 to FL 350 because it was to early for him due to still being to heavy.
The ATC controller said OK, maintain FL 330 then, and that was that.
I wasn't aware that an airliner such as an A340 could only fly to certain altitudes while still at certain weights. So this was interesting to hear and learn about. I guess it could climb higher later on after burning off some more fuel.
My questions are ............
How often do you think an airliner flight crew has to decline an ATC request for them to climb to a higher altitude because they're still to heavy?
When an airline dispatcher (or whoever) files an IFR flight plan with ATC for a certain aircraft, I guess the altitude they file for is affected by the aircraft's take-off weight, among other things. Is this true?
Bragi From Iceland, joined May 2001, 218 posts, RR: 0 Reply 1, posted (9 years 1 week 8 hours ago) and read 5918 times:
The A340 isn´t exactly known for it´s 'awesome' climbing performance .
Anyway, there is always a specific altitude for a given aircraft weight, where it is most economical to fly. - That altitude is known as optimum altitude.
Optimum altitude depends mainly on weight (also speed), and increases with decreasing weight. Take for example the B737-400, if the speed is Mach 0.74;
For cruise weight of 62.000kg, the opt. alt. is 31.500 feet, but when the weight is down to 50.000kg, the opt. alt. has gone to 36.000 feet.
(Those altitudes would be lower with Mach 0.78.)
Most aircraft simply don´t have enough power to climb altitudes much greater than opt. alt.
In an ideal world, all aircraft would constantly be flown at optimum alt., but then again, we don´t live in one, therefore step climbs are utilized.
In a step climb, you would climb above the optimum alt., fly "through" it, and then climb again as the fuel is burnt.
I hope this clarifies the matter.
Muhammad Ali: "Superman don’t need no seat belt." Flight Attendant: "Superman don’t need no airplane, either."
Prebennorholm From Denmark, joined Mar 2000, 6019 posts, RR: 55 Reply 3, posted (9 years 1 week 7 hours ago) and read 5874 times:
Bragi gave a very good explanation. All very long range airliners such as B747, A340 and B777 have an optimal altitude which vary many thousand feet according to the fuel load.
It was very likely an A340-300 on the Denver - Frankfurt route and it was still a very long way from home. FL330 is already a high altitude for a heavy 343. It would take a considerable time for it to climb to FL350 at max continuous power in the thin air up there.
Late into the flight, when weight is little more than half, then it is an entirely different story.
In general four engined planes like the A340 are less flexible in this respect since twins need to have more installed power in order to play safely at take off in case of an engine failure.
Quads benefit economically in some respects from needing less installed power than twins. If that wasn't the case, then there would have been much fewer quads out there.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
Goboeing From United States of America, joined Jun 2000, 2630 posts, RR: 12 Reply 4, posted (9 years 1 week 6 hours ago) and read 5842 times:
I have heard US Airways A-321s leaving PHL for the west coast say they are barely able to reach FL310!!! That thing must be a dog in the climb when heavy. Meanwhile the 757s going overhead from JFK to LAX climb immediately to FL390 and have received direct CIVET from while still in the climb.
Nick
Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Reply 5, posted (9 years 1 week 6 hours ago) and read 5834 times:
Hi guys.
>> Bragi, Zak, and Prebennorholm.
Thanks a lot guys for your answers & explanations. I wasn't aware of the fact that it's such a delicate balancing act between weight, airspeed, and altitude for airliners that are cruising at the high 30,000 feet+ flight levels.
Also, it's neat to learn about the method of using step climbs as fuel is slowly burned to reach the airliners optimum altitude.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 6, posted (9 years 1 week 5 hours ago) and read 5816 times:
If we look back at the rather early operations of jet transport aircraft, one would find several (rather too many) occasions when these aircraft were climbed far too high for a given weight.
The maneuvering margin with these early turboJET (not turbofan) aircraft could well be a problem at higher weights, as turboJET engines do much better at altitude than their slightly later turboFAN counterparts (speaking here JT3D vs JT4A), and the turbojet-powered aircraft would climb...and climb..until the maneuvering margin between low and high speed buffet was very small, which lead to jet upset incidents. The engines could GET you there, but the wing could not KEEP you there.
IN short...climb when the weight is absolutely correct, and NOT before....if you expect to collect your pension.
Fortunately, type conversion training covers this rather well, especially with FMS equipped aircraft.
Provided you pay attention.
Starlionblue From Hong Kong, joined Feb 2004, 15872 posts, RR: 66 Reply 7, posted (9 years 1 week 4 hours ago) and read 5786 times:
I have heard US Airways A-321s leaving PHL for the west coast say they are barely able to reach FL310!!! That thing must be a dog in the climb when heavy. Meanwhile the 757s going overhead from JFK to LAX climb immediately to FL390 and have received direct CIVET from while still in the climb.
Not to turn this into A vs B (let's leave that in Gen_Av) but the A321 is perhaps a more "optimized" solution than the 757, which is generally considered generously overpowered.
Like Viggen vs Gripen. Viggen was "maximal" while Gripen is "optimal".
411A, the classic example of what out are speaking of is the U-2 (TR-2), where the gap between mach buffet and stall was a mere 10 knots during cruise. And IIRC there was no autothrottle, simply a numb left arm!
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
NWA742 From , joined Dec 1969, posts, RR: Reply 9, posted (9 years 1 week 2 hours ago) and read 5725 times:
Not to turn this into A vs B (let's leave that in Gen_Av) but the A321 is perhaps a more "optimized" solution than the 757, which is generally considered generously overpowered.
Unless it presents a danger, you cannot put a blame to an aircraft for being overpowered. The 757 may be overpowered, but that is not a disadvantage at all. It's much more capable because of that very reason. Besides, if you suddenly need to get up quickly, you know you have the power to do it. I've heard a lot of pilots commend the 757 for it's performance and capability. Calling it overpowered is nothing but a complement in reality, my friend.
Actually, in a fair amount of cases, depending on engine type, A321's are more overpowered than a lot of 757's.
I'd like to hear why you think that is so, since almost all figures of power to weight ratios I've seen point that the 757 has a better PTWR than the A321, and the A320 for that matter.
Zak From Greenland, joined Sep 2003, 1993 posts, RR: 8 Reply 10, posted (9 years 6 days 19 hours ago) and read 5657 times:
"Unless it presents a danger, you cannot put a blame to an aircraft for being overpowered. The 757 may be overpowered, but that is not a disadvantage at all. It's much more capable because of that very reason."
yes that is usually a problem regarding efficiency. if you have lets say 50k lb excess engine thrust of what you on your plane would normally need, you are hauling around too heavy engines capable. lighter and cheaper engines would do hte same job for less money. so anything overpowered is not exactly something you want to have in civil aviation. efficiency is king, and having a plane with lots of thrust it doesnt need is not efficient, its a waste of money for the airline if they can order the same plane with smaller, lighter engines that are more suited for it(or another type that is less overpowered).
there are of course instances where power makes alot of sense, for example hot+high airports, however these are the exception and not the rule in most areas.
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 71 Reply 11, posted (9 years 6 days 16 hours ago) and read 5586 times:
As an old fighter pilot once said: "The only time a plane is overpowered is if you are going straight up at idle and it pulls the wings off."
Seriously, I used to teach B-727 initial for a company that had 727-100 (-7 engines) and 727-200 with -7, -15 or -17 power. Huge differences in performance but on a little thought, power does not solve all problems.
For example, where the -200 with -7 power labored for altitude with any kind of a load, the -17 engines would cheerfully push a heavy plane up to an altitude where the wings would no longer support it.
All aircraft designs are a compromise, and I've done step climbs in every type I've ever flown that was capable of three hours or more duration.
Happiness is not seeing another trite Ste. Maarten photo all week long.
Gigneil From United States of America, joined Nov 2002, 16215 posts, RR: 88 Reply 12, posted (9 years 6 days 12 hours ago) and read 5483 times:
For example, where the -200 with -7 power labored for altitude with any kind of a load, the -17 engines would cheerfully push a heavy plane up to an altitude where the wings would no longer support it.
This is a detail that's been overlooked to this point, SlamClick.
Altitude restrictions aren't always about power, they're frequently about hull/wing loading restrictions.
Ts-ior From Tunisia, joined Oct 2001, 3298 posts, RR: 7 Reply 13, posted (9 years 6 days 12 hours ago) and read 5480 times:
BA,VS,KL,AF,SA, SR,and Namibair South/East Africa-Europe flights change level when entring Tunis UIR,when they have lost weight due to fuel consumption.The same flights do not fly higher than FL310,or rarely 330,when they are heading south due to weight of course.
Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Reply 14, posted (9 years 6 days 11 hours ago) and read 5484 times:
Hi guys.
All of your info has been very intersting and great to learn about.
From now on, whenever I see an airliner's contrails high above me I'll have a greater respect for the measures that are taken to get it up there.
Now I know that airline pilots don't just take-off, set climb power and point the nose up untill they reach their desired altitude. It takes time and technique to get up there. The pilots have to wait untill their aircraft is ready to perform at the highest flight levels.
>> Starlionblue, with regards to the Lockheed U-2 Spyplane (aka "Dragon Lady"), I once read an article about it in Flying magazine and the gap between stall and mach buffet while cruising above 70,000 feet was referred to as "Coffin Corner!" and I believe the speed range was much less then 10 knots between stalling (where the nose would tuck under and the aircraft would desinigrate) and mach buffet. I'll try to find the article so I can check.
Bragi From Iceland, joined May 2001, 218 posts, RR: 0 Reply 15, posted (9 years 5 days 16 hours ago) and read 5318 times:
One of my instructors, on the written ATPL had an interesting story about this subject. Many years ago he was flying the DC-8 for a cargo airline, and regurlarly they had to fly a shipment of flowers from Africa to Germany.
Any delays would have cost the company a lot of money.
Before departure they were informed that due to traffic, they could only get FL290 or FL350, not FL330 as they had requested! (No RVSM at the time )
Selecting FL290 would force them to make a re-fueling stop along the way (not popular with management, and bad for the cargo), and FL350 was pretty close to the service ceiling of the DC-8.
Anyway, they decided to climb to FL350.
The airspeed had to be monitored closely, as there was small margin between low and high speed buffet (About 10-20 knots I think).
Another factor is, that as the load factor is increased, the stalling speed increases, therefore they were limited to a maximum of 5 degrees of bank!
Well before arriving at a waypoint, the autopilot had to be disconnected (as it banks the aircraft 20 degrees) and a very shallow turn started to maintain the correct airway.
He´s been flying for more than 30 years, and knows all kinds of stories!
Muhammad Ali: "Superman don’t need no seat belt." Flight Attendant: "Superman don’t need no airplane, either."
HaveBlue From United States of America, joined Jan 2004, 2069 posts, RR: 1 Reply 16, posted (9 years 5 days 14 hours ago) and read 5277 times:
Mr.Spaceman, I have read the same thing, where there was a smaller gap between the high speed buffet and the stall on the U-2, but Starlionblue is usually right on so I doubted my memory for a moment until I read your post
I'll try to find something to back that up. Either way, good thread and interesting posts by all.
XFSUgimpLB41X From United States of America, joined Aug 2000, 3958 posts, RR: 36 Reply 18, posted (9 years 5 days 11 hours ago) and read 5216 times:
Large airliners always use step climb techniques when going long distances. When I jumpseated on the 747-400..our initial altitude was typically about FL290-310...with a maximum capable altitude of about 330. Finally in the end of the flight, the airplane would end up sometimes as high as FL410. When a plane is heavy...they just dont handle the high altitudes as well.
A joke going around is that CRJ stands for "Climb Restricted Jet"...our engines have such a high bypass ratio and were made for a smaller airplane that we just dont have all that great climb performance when it is warm, we are heavy and get above the FL230's-ish. When we start tuckering around depends upon the weight and the temp.
Sponsor Message: 
From Canada, joined Mar 2001, 2780 posts, 
From Iceland, joined May 2001, 218 posts, 
.
From Greenland, joined Sep 2003, 1993 posts, 
From Denmark, joined Mar 2000, 6019 posts, 
From United States of America, joined Jun 2000, 2630 posts, 
That thing must be a dog in the climb when heavy. Meanwhile the 757s going overhead from JFK to LAX climb immediately to FL390 and have received direct CIVET from while still in the climb. 
From Hong Kong, joined Feb 2004, 15872 posts, 
From , joined Dec 1969, posts, 
From Tunisia, joined Oct 2001, 3298 posts, 
From Germany, joined May 2004, 115 posts, 
From , joined Dec 1969, posts, 
Sponsor Message: 
Printer friendly format
