Why a 3rd FMS?

PHX767

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Why do some long range corporate planes have a 3rd FMS? In the overwater airliners I have flown, they have 3 IRU's and 2 FMS. I am looking at the specs for a variety of biz jets and see that a lot of them have 2 IRU's and 3 FMS. Can't seem to figure this out on my own. Obviously this is a reduncancy (sp?) issue, but not a requirement. Looked over the NAT manual and see the requirement for 2 long range nav systems, is this just a way to dispatch with part of the nav system mel'd?

What is the value/return on investment on the 3rd FMS vs. other equipment. The SATCOM seems to be a great idea, but what about that against a 2nd HF, etc?

Thanks in advance for the info. Got some good info from the discussion on MNPS and NAT in the past few days, thanks.
 

G100driver

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With 3 FMS's you should not ever get stuck crossing a large body of water. We had one FMS fail on us getting ready to go to HI. You cannot MEL an FMS priror to entering RNP-10 airspace. The flight was canceled needless to say. (At least we could not (135). I am sure someone will correct me if I am wrong :))

For some folks, it is worth the cost I guess.
 

empenage

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We have 3 FMS, 3 IRU, 3 HF, 2 GPS, 1 SATCOM and a partrige in a pear tree.

Load'er up baby.
 
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fokkerjet

Why 3? Because it looks really cool to get a triple FMS failure when you did something stupid like request NOTAMS along your route:uzi: You can't pay for that much excitement, especially if it happens at 30W!
 

sydeseet

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Burp, why not?????

(Name the movie)
 

Gulfstream 200

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PHX767 said:
Why do some long range corporate planes have a 3rd FMS? In the overwater airliners I have flown, they have 3 IRU's and 2 FMS. I am looking at the specs for a variety of biz jets and see that a lot of them have 2 IRU's and 3 FMS. Can't seem to figure this out on my own. Obviously this is a reduncancy (sp?) issue, but not a requirement. Looked over the NAT manual and see the requirement for 2 long range nav systems, is this just a way to dispatch with part of the nav system mel'd?

What is the value/return on investment on the 3rd FMS vs. other equipment. The SATCOM seems to be a great idea, but what about that against a 2nd HF, etc?

Thanks in advance for the info. Got some good info from the discussion on MNPS and NAT in the past few days, thanks.

You can cross the lonely dark North Atlantic (or Pacific) with the bare bones equipment and save a few bucks, or you can have everything possible at your disposal....

the choice is yours.

I know which one I would want my crews having if they operated under these conditions....

Think resale - outfit your long range aircraft the same way everyone else's is --- to the max.

3 FMSs
3 IRUS

(and a forward crew lav)
 

G100driver

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fokkerjet said:
Why 3? Because it looks really cool to get a triple FMS failure when you did something stupid like request NOTAMS along your route:uzi: You can't pay for that much excitement, especially if it happens at 30W!
Why miseur (heavy frog accent), it is because we designed it that way.
 

rice

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Gulfstream 200 said:
You can cross the lonely dark North Atlantic (or Pacific) with the bare bones equipment and save a few bucks, or you can have everything possible at your disposal....

the choice is yours.

I know which one I would want my crews having if they operated under these conditions....

Think resale - outfit your long range aircraft the same way everyone else's is --- to the max.

3 FMSs
3 IRUS

(and a forward crew lav)

Absolutely, positively will not fly without that!!!!!!!!! Nothing more important when 5 hrs into the trip and you get up just to find out that Mr. and Mrs. Rich are racked out in the back and blocking access to the lav:( .
 

Lead Sled

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> enuf
You're flying along fat, dumb, and happy out over water, a long way from land with your dual FMSes. One of them takes a dump and dies on you. Not a problem, you still have the other.

Same scenario, different day...

Your flying along, FD&H, and your dual FMSes begine to tell you two different things. It's like the old Chinese proverb - "Man with one watch knows what time it is. Man with two watches is never sure." The third FMS is basically a "tie breaker".

Personally, when I fly oceanic, I also carry a handheld GPS. I'm not too good with a sextant.

'Sled
 

Lead Sled

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rice said:
Absolutely, positively will not fly without that!!!!!!!!! Nothing more important when 5 hrs into the trip and you get up just to find out that Mr. and Mrs. Rich are racked out in the back and blocking access to the lav:( .
Or you could just do what the guy I fly with does and pee in the sink. :0

'Sled
 

Kingairrick

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sydeseet said:
Burp, why not?????

(Name the movie)
Animal House

Also: why can't you cross fill the perf init to FMS3 like you can between 1 and 2?
 

PHX767

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Thanks, Sled. That makes a lot of sense. In the days before FMS (gasp!) we triple mixed the 3 IRS's. If one of them wandered away from the others we could take it out of the mix and still be fairly accurate.

But dude! That avatar..... :eek:
 

Gumby

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rice said:
Absolutely, positively will not fly without that!!!!!!!!! Nothing more important when 5 hrs into the trip and you get up just to find out that Mr. and Mrs. Rich are racked out in the back and blocking access to the lav:( .
Especially when one wants to "punch it" in private!!:eek:
 

rice

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Lead Sled said:
Or you could just do what the guy I fly with does and pee in the sink. :0

'Sled

I didn't know you flew with Gumby??? BTW does he know you're using his pic for your Avatar now :D .
 

G100driver

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Sled, gotta love that avatar. That is the reason why NO ONE should date someone they met on the internet.
 

h25b

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.....
Lead Sled gets the award for the most visually offensive avatar. Congrats!

The forward lav I can tell you would be a must for me having done 5 1/2 hour legs in the Hawker back and forth to the west coast. The pax always liked to set up an obstacle course for you before falling asleep, then you get hop-scotch over all the briefcases in the aisle. I can't imagine what that would be like on a 10+ hour haul...:(
 
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