Night island flying

Scenario:

You depart airport at 2000 local for a 4.6 hour flight to a remote island. Island has no divert. Divert is to return to origin. Any other divert results in newspapers and "international incident". Island has no NAVAID. Weather is only available by the controlling agency on the field, which cannot be contacted until inside of 200nm. Everything outside of that is non-radar, and due regard. The ASOS on the field has been known to be slightly "off", but the controllers on the field can give you accurate wx. You're flying an airplane that has dual GPS. You're 3.8 into the flight and lose one of the GPS's. What do you do and why?

Acft type: DC-8 with CFM's. Fuel is no factor (Enough for RTB, and mins.)

Ask if you need more info, obviously.

Forecast?

Fuel on board?

How long until I can talk to local controller, I must be getting pretty close to 200nm with .8 to go?

Can't think of too many reasons I wouldn't continue... I mean it's just a redundant nav failure.

You have another ~3.8 of fuel to get back to dry land? You sure its even an option at this point to 180?

Continue. Land. Go to bed. Do it all again tomorrow.

I'm not very experienced with regards to ETOPS. However if I had less than an hour to go I'd say it was safer to continue to the destination.

If you lost the second GPS would it be safer to fly over another 4 hours over open ocean? Put the compass on the big E or W and keep your fingers crossed? The sailor in me is cautiously optimistic (sounds like an adventure) the pilot side is all "hell nah!"

My airplane has equal time points, assuming I was 3.8 hours into the flight we would be forced to continue anyway. Not that flying to such a location would be approved (no nav aid, no wx, no alternate). Again it sounds like a fun adventure but rational planning dictates a big NO, at least for 135 ops.

Forecast is standard for the area. Clear through the day, late afternoon drizzle with 1500' cigs, clearing at night. 050SCT at ETA.

Fuel on board; enough to make the 180 and return, if necessary. Aircraft type is DC-8 with the CFM's. So.... .75, maybe?

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Fuel is not an issue.

No factor on ETOPS. 4 holer in this one.

The forecast is contracted from another location.... in Japan. But never accurate. May as well be holding a finger up outside. We had been forecasted to be CAVU (with chance of pm rain) for the next 72 hours. A cyclone rolled in and shut everything down for 5 days.

I especially want to know your take on this scenario, please.

Also, is there a difference between INS, FMS, and GPS? Mind explaining?

Does the FMS tie-in to the INS?

Nope. It was a scenario I faced flying back from leave. Departed Singapore at 2000, and headed to DG. Looked at my watch and knew we were about an hour out. Plane started a shallow right turn, and the Capt. came up on PA. Said he'd lost one of the Navs (not sure if it was INS, or GPS, but fairly sure he said GPS), and that we were turning around and heading back to Sing as there were no agreements in place, and there was no one to fix the plane. And then the issue of what to do with the pax....active duty service people, contractors, and 3rd country nationals.

The majority of the trip back to Sing was me talking with a pilot and a fellow controller about why they would 180.

So, we landed in Sing, got put up in a hotel, and flew back out the next morning in a 17 with webbing seats.

Rummaging around in the cockpit, I know they had dual FMS's, and I would think?, GPS's tied into them.

Here's the airplane:

http://www.airliners.net/photo/Air-...91750/L/&sid=b67fa70c273c9a1b1365d69580132bf9
http://www.airliners.net/photo/Air-Transport-International/McDonnell-Douglas-DC-8-
72CF/2129589/L/&sid=b67fa70c273c9a1b1365d69580132bf9

Well as someone who learned celestial I agree. However, when you learn to think like a pilot in the present and consider explaining your actions to the CP or consider your opsecs, well adventure time is over.

On the other hand, one of my favorite places in SF is the memorial to those lost at sea during WW2 in the Pacific. It gives one pause. Most of the dudes were Army Aviators.

I'd have to go look into our systems manual to make sure, but even on the Dash's FMS's we have two GPS inputs, one IRS input and two VOR/DME inputs. All cross reference each other to come up with a best computed position. Often results in ANP of .01.

It could have been a mel issue. They could safely continue to DG with one GPS system down, but wouldn't be able to depart with only one nav sytem for the return leg. Without looking at the MEL, that's just a guess. Usually the FE at supplemental carriers have A&Ps to deal with these situations(or a mechanic onboard), but who knows what they had in their fly away kit? The Captain could have made the decision on his own with the crew, but probably phone patched the company for their input too.
I plumbed on the -10 and 74 but never on the -8. Did some maintenance on them back in the stone ages before GPS though.
Slemers

I knew this had to be Diego.

3.8 hours into a 4.6 flight? I'd consider it safe to continue, but that's based on knowledge of my aircraft. The IRUs won't drift significantly in 0.8 hours, even without a position fix from the GPS or DME/DME. But again, I have no knowledge of the DC-8, and for them it may have been better to turn around. There is absolutely no need to jeopardize safety or put the crew in a legal situation just to complete the mission.

And sorry @MikeD, I'm a young whippersnapper.

Random aside since ETOPS was brought up: In my two-engine jet, if you're inside of an hour, you've already exited ETOPS. Not a factor.