Question about flying over the Pacific

You just picked about the longest regularly used air route (2245 nm, 2561 mi) with no alternates. White Shark breeding ground about half way there too, just to make it more interesting.

 

as close to a commercial shipping lane as I could get it to

 

I'm not an airline guy, but I have made a fair number of crossings on that route. It's not that complicated. You figure out (or in an airline case, dispatch figures out) your equal time points on the crossing, from the nearest airports. Not equal distance-- if you have a strong tailwind going one way and turn around, you'll have a strong headwind, so the distance will be different than the time.

Then you compute how much fuel you would have when arriving at each alternate, from the equal time point-- which is the worst case scenario. On either side of the equal time point, you are better off. Typically, you compute loss of an engine, loss of pressurization, and divert at cruise altitude. Usually in regard to fuel, loss of pressurization is the worst one because it requires a descent.

If your flight plan shows that you don't have enough fuel in one of those scenarios, that is known as a "wet footprint" and most people try to avoid that. I don't know if the airlines are allowed to have a wet footprint, but I generally flew airplanes that didn't have one.

Then, you can get into ETOPS (which is "Extended Twin Engine Operations"), really an airline thing that I never had to deal with. They have something like 180 minute ETOPS, so they have to be within 180 minutes of an alternate if they are using a twin engine airplane, which most of them do.

 

More fun is when you are going to some place like Easter Island, where there is only a single runway and truly no alternates. There you calculate a "Point of No Return" or PNR, where you are now committed to going on.

 

Don- Yup, Hawaii may be a long ways, but there are plenty of runways once you get there. Same for LA.

 

You gotta rely on ETOPS ! Engines Turn Or People Swim.

 

I’ve flown right over the North Pole.

Matt

 

One more consideration in the calculations - IF the aircraft has a chemical generator passenger oxygen system it means that the remainder of the flight has to be made at about 15,000 ft after the generators run out of their limited oxygen supply.

 

could a jetliner realistically glide into the ocean? similar to the river landing that was famous a few yrs ago.

 

Depends on the sea state

 

If you have to ditch, sea state is irrelevant to the decision because you are going down anyway. If memory serves me, land parallel to the waves on a crest if windspeed is not a large factor.

 

Rough calculations say that you can glide about 150 miles if you carefully use the L/D of the airplane. A 777 has a RAT that will provide hydraulic system pressure to essential controls so a smooth controllable landing might be possible. The airplane has rafts and fish food to throw out after you are safely aboard the raft.

 

Bob; I thought the fish food was aboard the raft..........

 

Most of the over water stuff I have done is in business jets, and in some cases we had additional oxygen capability, and in some cases we didn't. When we didn't, we had to run the plans at 15,000, otherwise they were run at 20,000. Descend either way.

 

Large aircraft haven't had a great track record in terms of ditching, so I would guess in the ocean most likely it would break in half, but you never know until you try!

 

These guys did it:

https://en.wikipedia.org/wiki/Air_Transat_Flight_236

Also google the "Gimli Glider" although in their case, they were over land.

 

Interesting that in both of the "glider" cases, the pilots were experienced glider pilots.

 

Hi Matt

That sounds interesting and worth of a story, how did it go?

Cheers

 

It was wonderful. Much more luxurious than adventurous. The Cathay Pacific direct flight from New York to Hong Kong. It flies like this:

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I recommend business class. It's a long trip.

But there are very, very few alternative opportunities to land for a long section of the flight, back to the OP's question.

Matt

 

Yup, and that Mercator really distorts the route. Greenland (836,000 sq mi) being bigger than the US (3,800,000 sq mi) is a pretty good indicator of how distorted.

 

Seychelles is fun like that if you are flying down the Red Sea and then around the Horn of Africa. During the final stages of the flight the only alternate is in Somalia.