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Still-air Range SFO/LAX-SIN  
User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Posted (8 years 3 months 4 days 21 hours ago) and read 3824 times:

What still-air range would an airliner need to fly westbound SFO-SIN and LAX-SIN year-round without a technical stop?

5 replies: All unread, jump to last
 
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 3 months 4 days 19 hours ago) and read 3778 times:

KSFO-WSSS 7340NM (NO WIND)
KLAX-WSSS 7621NM (NO WIND)

The wind factor will vary considerably. This time of year you are most likely looking at a -70Knot factor the entire route, while in the summer it might be as low as -30Knots.


User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 2, posted (8 years 3 months 4 days 1 hour ago) and read 3666 times:

A 70 knot headwind along the entire route would add about 1000nm to the still-air distance, right? So, an airliner would need a still-air range of more than 8500nm to fly LAX-SIN nonstop in the winter, right?

User currently offlineBAW716 From United States of America, joined Nov 2003, 2026 posts, RR: 27
Reply 3, posted (8 years 3 months 3 days 21 hours ago) and read 3617 times:

Divide great circle distance by average speed (M0.84 at FL390 is about 490kts), so 7340/490=14.97hrs. Add 70kt headwind brings ground speed to 420kts. 7340/420=17.48hrs. Take the still air ground speed and multiply times the endurance based on wind and you get the adjusted distance: 490 x 17.48hrs = 8565nm.

You pretty much hit it on the nose.

baw716



David L. Lamb, fmr Area Mgr Alitalia SFO 1998-2002, fmr Regional Analyst SFO-UAL 1992-1998
User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 4, posted (8 years 3 months 3 days 19 hours ago) and read 3596 times:

Thanks baw716. So, we have equivalent still-air distances of 8565nm for SFO-SIN and 8891nm for LAX-SIN by the same methodology. It seems like LAX-SIN is nearly as challenging as EWR-SIN.

User currently offlineBAW716 From United States of America, joined Nov 2003, 2026 posts, RR: 27
Reply 5, posted (8 years 3 months 3 days 8 hours ago) and read 3515 times:

Zvezda, each of these flights presents its own unique set of challenges.

LAX-SIN, for example, is pretty much flown on a straight line track toward HKG NW over the Gulf of Alaska, crossing the Aleutian peninsula at about 59N160W, then crossing over the Kamchatka peninsula, entering China at 52.5N140E on a straight line track toward HKG, then direct to Hoh Chi Minh City (SGN) and into SIN.

In projecting this course out over todays upper atmosphere weather projection (ended 1800z23Jan), it crosses two jet streams at 50N and again at 55N (the first at FL330 at a 90 degree angle (100kts), the second (much stronger one 160kts) at FL280 with an area of moderate turbulence that extends for about 200 miles before crossing the Aleutian chain. After that, it encounters another jetstream at a 90 degree angle just over Kamchatka (FL260 at 90kts), then pretty clear sailing until hitting the subtropical jet at FL350 (170kts) at 34N118E. After that, its pretty clear until Singapore. This particular track requires flying over jetstreams crossing at right angles, which really has an impact on heading vs. track. This degree of weather requires additional fuel to compensate for the degree of crosswind component at upper altitudes. Alternate airport planning is not a horrible consideration on this route, since SEA, ANC, Magadan, Beijing, Shanghai and HKG are within 200 miles either side of the projected straight line track. All are within easy reach in a one engine out scenario.

EWR-SIN on the other hand does not have the issues with the jetstreams, since it pretty much goes straight up over the pole (straight line from EWR up over eastern Canada, Baffin Island and over Thule Air Base in Greenland before crossing the "polar zone" north of 80N. Here, navigation gets tricky because you set up a heading of 010 leaving Thule and cross over the pole, arriving on the other side on a course heading of 160. While this area is only about 500 miles across if that, GPS is pretty useless that far north. The good news is that they miss the magnetic north zone over Northern Canada, which allows them to fly magnetic tracks up to the polar zone, then true tracks above 80N, then magnetic tracks once they hit about 80N on the other side. There is little to no jetstreams at these latitudes, just cold air. Clear air turbulence (CAT) can be a problem in these areas, but with careful planning, then can avoid areas of temperature variation, which is the big precursor for determining CAT. In addition, up that far, there are specific polar tracks which must be flown due to the navigational challenges of coming within two degrees of true north. On this track, they don't hit a jetstream until close to 30N103E, where there is about a 100mi area of turbulence crossing the same jetstream that the LAX-SIN flight would encounter quite farther east.

As for suitable alternates, going this route, after Montreal is Frobisher Bay, then Thule, the long stretch is between Thule and Irkutsk, then Beijing (far east), Hanoi, tracking between Bangkok and Hoh Chi Minh (about half way between) then across the Gulf of Thailand into Singapore.

It is important to note that these are WESTBOUND routings. Eastbound routings tend to go further east to take advantage of the tailwinds that occur with the natural routing of the jetstream. This is true for both the EWR and LAX flights, the Eastbound EWR routing would be much closer to the track for the westbound LAX flight, with a slight left turn over the Aleutians to pick up the eastbound jetstream over northern Canada and Hudson Bay.

The difference between the westbound and eastbound flights can be significant; up to two hours on the LAX flight and closer to three on the EWR flight. The average flight times LAX-SIN run about 17.5 hrs, EWR an hour longer, eastbound, SIN-LAX can take as little as 14.5 hrs and EWR about 15.5-16hrs.

Singapore Airlines specifically designed their A345s for this kind of flying. It would be impossible to fly these routes with the A345 at or near full payload capacity. Hence, with only about 150 seats on the aircraft instead of 250, the lighter payload allows them to carry the additional fuel required to make the trip and have adequate reserves at both ends.

I have flown these flights in a simulated environment. They are a bear, especially flying in the Polar regions where navigation becomes the number one issue. However, the A345 in their configuration makes it with about 20-30k lbs of fuel to spare on either end. The crew rest requirements must be substantial as is the workload. For a flight that long, three full meals would need to be served as well as a LOT of provisioning for liquids. The upside of the SQ operation is that the seating on the aircraft is reported to be very comfortable, even in Executive Economy. The additional seat pitch and recline allow for adequate movement, which of course cuts down on issues of DVT.

I can send you the specific weather charts with the straight line routings I plotted with the alternate airports circled along the way. It makes for interesting study. The actual flight plans are never straight line routings; however, to save time, this was a good approximation.

I hope this helped to understand the flight planning aspects of the questions you ask about the SQ flights; while they are challenging to operate, the routings do not change radically, since wind patterns in these particular regions tend not to change radically. The only exception to this is flying between the west coast of the US and Alaska, when the prevailing winds can come from your back or your nose, pushing you right or left of course depending on the direction of the flight.

Just as an aside, for a long time, Continental flew EWR-HKG (don't know if they still do), via the Polar 1 routing with a 777-200ER. Since the track was further west than the SQ track, they could stay within the ETOPS 180 rule over the polar regions; Thule on one side and Fairbanks on the other, then Magadan and Kharbarovsk on the other side of the pole are within 180min of the HKG polar tracks (which is the ETOPS critical portion of the flight). EWR-HKG is near the outside range of the 777-200ER, but still within acceptable limits.

All the same, flying on these polar routings, as much as I love the 777 and trust its engines, having four engines going literally across the North Pole is a little more comforting. I am certain the SQ folks think the same thing.

baw716



David L. Lamb, fmr Area Mgr Alitalia SFO 1998-2002, fmr Regional Analyst SFO-UAL 1992-1998
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