B777 cruise
 

Hello everyone,

I am kind of a puzzled by this. Was at Changi Airport yesterday night. SQ36 (B777-212ER) was operating a flight from SIN-AMS. In its ATC clearance, controllers
assigned SQ 36 to cruise at FL280 M.84 on the speed, but however, the pilot said that he could only go at Mach.80. Why can't he go at Mach.84 while 15 minutes ago an Air France B777 can accept Mach.84 at FL280 as assigned. The reason controllers try to assign the higest speed possible because of the huge amount of flights departing around the same hour mainly using the same route to Europe. In the end, the ATC controller had to delay all of the rests of the European B744 flights because their minimum cruising speed was at .84 or higer. All the European flights behind SQ 36 went to company frequency to request a change of flight plan to lessen the delays but was denied because they don't want any planes to fly over the Iranian and Afghanistan airspace. SQ 26 was the worst affected, departed Singapore 2 hrs 15mins late. Things can be as bad that the pilots chose to disembark passengers for the 1+ hour wait.

Normally, these European flights uses the same airway, so they got to go in the sequence with 10 minutes to seperate each departure in ATC clearance. If you have to depart 10 minutes behind a flight which has gate real far from the runway, you can only start you push back once that flight has reached the holding point, which is obviously more than 10 minutes of wait. Other European flights, even got the clearance at the same time as the others, but time adds up ( 10 mins behind... which is in return 10 mins behind.... which is also 10 mins behind...) and to add up the push and start and taxi time of those, you know how bad it is.

For the SQ 36 case, the next flight behind him got to choose to depart 19 mins behind him (differ speeds) or 10 mins behind him but forced to cruise at .82. In this sense, it will add time which means delays to other flights. A flight may be ready for push exactly on time but it is possible he will leave an hour later.

SIA flights to Europe are normally never on time and here's why.

alvin

Any idea why SQ 36 had to go at .80? It has definately delayed every other flights.

Thanks
alvin

:)

I don't have the exact figures to hand but using rules of thumb at FL280, M0.84 could end up very close to, or even over, the B777 normal Vmo of 330Kts, so the a/c might have been unable to cruise at that mach. I also believe some 777's are certified at 350Kts/M0.89 - possibly those of AF.

If you put your Mach No pointer on your Jepp Computer against M.84 andlook at the CAS at a PA of FL 280 you get 336Kts CAS

Everytime I go, AF always managed to go Mach.84. SQ's seldom managed to, mainly at about.81. Cost index?

alvin

I reckon the crew on that flight do not want
to compromise on fuel.For 777 going from SIN to Europe must have had almost max=min fuel.
Thus given cost index between 20~50,M.80 sounds ECON CRZ from FMC,My guess is that they want to mantain this speed in order to
conserve fuel.If they're poker player(like me),they could have accepted M.84 atFL280,
then ask for climb once under Chennai radar
(3.5 hours later)or Muscat radar(6.5hours later).

Management is mean,thus fuel available is lean. :p

Thanks for the reply. But if they cannnot get clearance for higher levels, do they cruise Mach.80 all the way? I have heard from quite a few pilots that they can only maintain FL280 till Europe sometimes!

alvin

Yes, the B777-300 has a Vmo of 0.89M

Aerodynamically I don't see how 777-200ER can be certified to different speeds, having the same body and wing. Nominally 330/0.87M

I have always heard the 747-400 making 0.86M at FL280 too at ISA >+15. Wonder what kind of IAS these work out to be.

Can those guys really make it at FL280 .84/.86 for the B777-200ER and B747-400 respectively.

Might be a case of lie first,get the clearance and sort it out later, maybe a tad slower, no worries.

Another factor is the weight too.

Typo edit
:)

[ 28 November 2001: Message edited by: 7times7 ]

M.86 at FL 280 results in a CAS of about 345kts and at FL 350 about 295kts. Since the airloads on the airframe depend on CAS it seems that prolonged or sustained operation at lower levels must involve a fatigue life penalty. Also the ride at 345 kts if turbulence is encountered must be interesting. The lower CAS at FL350 is closer to turbulence speed; if lower levels must be held and the likelihood of turbulence is there a lower speed may be prudent.

I understand that if you pay Boeing a certain amount of money ($1m+ I hear) they will up your Vmo by 20kts & Mmo by .02M.
Just a small software change, nothing to do with the airframe, but you are getting a 'competitive advantage'

By the way,could anyone on the 777ER tell me
what is the max structural take off weight,what is the max fuel capacity and what
engine(RR?)thrust rating does SQ has?
Thanks.

I think the B777-200ER has a max take off weight of 656,000 lbs. Singapore Airlines' 9V-SQ series B777s are powered by Trent 884, with 84,000 pounds of thrust each, 9V-SR/9V-SY/9V-SV are powered by Trent 892.. powered by 90,000 pounds each i think.

alvin

YOU THINK!! You mean you dont know..tsk.tsk.
Walt,,, :D

Hi Guys. Our 777-200IGW max structual takeoff mass is 294835kg or 652000 pounds. that is with the GE90-90B, 900000 pounds of takeoff thrust. Came back this morning with max ZFM, min block fuel WMKK-LOWW 100200kg, actual takeoff weight 294630kg. Econ cruise cost index 56 results in .807 at FL280. Managed to get up to 310 with Bombay.

Hmmmm a 777 with 900000lbs on each wing id like to see that.. Similar performance to the space shuttle straight into outer space..... May need some serious mods for exceeding mn or seriously throttled back!!! :rolleyes: :p

OK i was obviously jet-laged when writing the post. How about 90.000 pounds? :p

Cruise at any speed you like. :D

boeing772er Someone correct me please if I am wrong, but aren't the last two digits of the engine designation the thrust rating?

Example: RR Trent 884 = 84,000 lbs thrust
RR Trent 892 = 92,000 lbs thrust

Another exmample: P&W 4152 = 52,000 lbs thrust (in this case the engine series is 4 = 4000, the airframe is 1 = Airbus.

Just curious guys. :)

Yes. For P&W, four-digit engines are for large commercial aircraft. The first digit is the series, the second digit is application (0 [and sometimes 2] for Boeing, 1 for Airbus, 4 for McDonnel Douglas), and the last two digits are thrust in K-lb.

For R-R, the first digit is the series, and the last two digits are thrust in K-lb (shouldn't it be in KN :D ?).

For GE, only the GE90 has thrust rating as a part of the engine model, for example, the GE90-94B is a 94K-lb thrust engine, and the B stands for Boeing.

Actually you have a point, but I got these figures from the B777 tech manual of SQ.

alvin

Boeing772er: you might not be wrong. SQ might have Trent 892 derated to 90K.