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Joined: Fri Sep 17, 2004 5:54 am

How Do You Fly A Plane Without FMC?

Fri Oct 01, 2004 12:40 pm

OK I had a thread that I posted before with the 747-300's and that there were rumors that the FMC wasn't reliable. This was the case with JAL and I heard of it going off course many times. SO I asked how reliable the FMC was for the 200's and I get a response. The 200 does not have FMC's. That is the same thing that I heard today when I was in an aviation store that the 200 does not have FMC. If there is no FMC, how do the pilots fly? I mean do they have to do anything manually or setset each VOR after passing it? I have no idea how that type of aircraft can fly. Or am I misinformed?
Flown on: DC-10-30, B747-200B, B747-300, B747-300SR, B747-400, B747-400D, B767-300, B777-200, B777-200ER, B777-300
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RE: How Do You Fly A Plane Without FMC?

Fri Oct 01, 2004 2:05 pm

When the 200/300 were produced by Boeing, there was not a FMC. The primary means of navigation was via an INS (Inertial Nav System). There were several options with Delco and Litton(72/92) being the two systems I am familiar with. In addition to providing navigation, the INS supplies gyro platform, radar stabilization and a few other things.

Honeywell offered the FMS as an add-on and several airlines installed the FMS. As far as the FMS not being reliable, that's news to me. I have flown both the 200 and 300 and found them very reliable, not as accurate as the 400 but certainly very acceptable.

Without the FMS, the navigation was done by the INS. Depending on the nav system, you either loaded the waypoints with the lat/long or there was a database and all you had to do was use the identifier to load the waypoint. In US or Europe airspace, you did have to tune the VOR for the specific airway you were on.
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RE: How Do You Fly A Plane Without FMC?

Fri Oct 01, 2004 2:12 pm

If there is no FMC, how do the pilots fly? I mean do they have to do anything manually or setset each VOR after passing it? I have no idea how that type of aircraft can fly. Or am I misinformed?

Understand that the vast majority of airplanes of all types flying worldwide do not have FMC's. You fly a Cessna 172, you're not going to have an FMC. Most airliners in service probably still do not have FMC's if you're talking worldwide (modern airliners do have FMC's, but a lot of airlines around the world don't fly the most modern planes). This includes most 747-100's, 747-200's and 747-300's, unless they've had their cockpits upgraded.

Yes, with no FMC you set your radios manually. This is not that big of a deal, honestly; it's just turning a dial or punching in a couple numbers every once in a while (usually every 30 minutes to an hour or so, though it depends on what part of the world you're in). I believe some older airliners had FMS's (not FMC's) that would auto-tune radios when on auto-pilot set to inertial nav, but these were not full-blown FMC's.

Every pilot is still trained on how to use VOR navigation and how to set his radios himself. It's a trivial thing to learn and manual navigation can still be used in an airplane with FMC if something happens to the FMC.

The main function of an FMC is actually not to set radios; if that was all it did, it would be a pretty pointless device. The FMC is a sophisticated computer system; it does a whole lot of things, and its main function is to reduce pilot workload and increase airplane efficiency. Most of the things the FMC does (calculating V speeds, takeoff power settings, top of descent, climb, cruise and descent speeds, fuel usage, etc.) used to be accomplished by the flight engineer - this is why FMC-equipped cockpits only require two pilots vs. the three that was common in the old days.

But everything that an FMC does can be done manually. The FMC, like all computers, is really just doing a lot of math on a continuous basis and then feeding that data to the auto-pilot and/or the flight director, along with making sure all the important systems on the plane are operating normally. You can do all that math yourself, and you can scan all those instruments yourself, it's just going to take you longer to do it and it's going to pull you away from other tasks and reduce your situational awareness.

Changing radio frequencies and navigating manually by VOR is probably the least labor-intensive task for a pilot that the FMC has taken over.
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