Flight Management Computer (FMC)

Old Feb 13, 17, 2:20 pm
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Flight Management Computer (FMC)

In the thread about BA1 getting 'lost' in Shannon, this comment by Snafu_again caught my attention:

Originally Posted by Snafu_again View Post
How is the data uploaded to the FMC ? .... would you believe from a 3.5 inch floppy disk ! (and they cause no end of problems (more the loading machines rather than the disks)). Why not USB or Memory Cards ? Because of the cost. Modifying the aircraft, certification etc.
Aside from being mildly amusing (another interesting recent use for 3.5" floppy disks includes Norway's doctors, which ended in 2015), this got me thinking about the Flight Management Computers in use on airliners. I did have a quick look to see whether this had been covered before, but didn't find anything, so…

1) What kind of computation does an FMC do? Do these tasks vary significantly between different (sub)-types of aircraft, families of aircraft, or even individual airlines? I assume there are lots of 'keeping the plane running' tasks that are involved – e.g. balancing fuel between tanks, handling conflicts between information from redundant sets of equipment, etc.

2) What kind of hardware and software do FMCs run? Presumably they need to be specially hardened and certified, but how 'current' are they, given the long lead time between designing and certifying the plane, it entering service, and the lifetime of the airframe itself?

3) How involved is BA/BA engineering in the specification of such FMCs, or is it 'standard' from the aircraft manufacturer (linked to Q1 above).
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Old Feb 13, 17, 4:09 pm
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Think of the FMS as the operating system. Depending on the plane you buy you can have one that the aircraft manufacturer specifies for you (which is the most common arrangement) or you can choose from two types that the manufacturer has cleared for use (as on a320 for instance) and which one you choose depends on price/functions/commonality with whatever else your airline operates.

They are updated regularly but, as you might expect, the software has to be very robustly tested before it is cleared for Flight and this tends to be the limiting factor on how often they have new releases. As a result Airlines have introduced EFBs as a complement to the FMS which can be updated more quickly but are not certified to the same level.

New FMS are designed with loads of spare processing power and memory but over 20 years+ this gets filled up with more stuff and it is not unheard of to then upgrade them. However this can be a very expensive process so the main focus is on optimising what you have already fitted and shifting some calculations to the EFB before using the FMS for final check/input.

Airlines can really personalise the EFBs but have less direct design input to the FMS.

I'm sure a pilot will be along shortly to give an expert view...

Last edited by Robespierre; Feb 14, 17 at 12:55 pm
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Old Feb 13, 17, 4:13 pm
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The launch crews in the Minuteman III silos still decrypt their launch orders (please God no) using 8-inch floppies.
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Old Feb 13, 17, 4:17 pm
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This is probably best moved into the Ask the Staffer thread which is monitored by a few BA Professional Pilots who post here.
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Old Feb 13, 17, 4:23 pm
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There are basically two operating systems: Boeing and Airbus. Within they it's pretty standard. As far as I'm aware the route is either input manually or loaded from datalink which is sent by the company dispatch.
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Old Feb 14, 17, 11:16 am
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Originally Posted by Robespierre View Post
...Airlines have introduced EFBs as a complement to the FMS which can be updated more quickly but are not certified to the same level.
EFBs are Electronic Flight Bags aren't they? (Tablets, etc).
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Old Feb 14, 17, 11:28 am
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Originally Posted by JAXBA View Post
EFBs are Electronic Flight Bags aren't they? (Tablets, etc).
Yes. I think on some aircraft they are built in (787 for example), but mostly are just on a tablet attached at the side like here:



The EFB has charts, route information, and lots of manuals and company procedure documents on. I think the only document which is still physically carried is the quick reference handbook (QRH).
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Old Feb 14, 17, 12:00 pm
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Originally Posted by KARFA View Post

The EFB has charts, route information, and lots of manuals and company procedure documents on. I think the only document which is still physically carried is the quick reference handbook (QRH).
...And the tech log!
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Old Feb 14, 17, 12:02 pm
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Originally Posted by 13900 View Post
...And the tech log!
Ah of course, yes.

I think some airlines have gone to an electronic tech log? I may be completely wrong on this, I have some vague memory of seeing this somewhere.
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Old Feb 14, 17, 1:06 pm
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Originally Posted by squawk View Post
1) What kind of computation does an FMC do? Do these tasks vary significantly between different (sub)-types of aircraft, families of aircraft, or even individual airlines? I assume there are lots of 'keeping the plane running' tasks that are involved – e.g. balancing fuel between tanks, handling conflicts between information from redundant sets of equipment, etc.

2) What kind of hardware and software do FMCs run? Presumably they need to be specially hardened and certified, but how 'current' are they, given the long lead time between designing and certifying the plane, it entering service, and the lifetime of the airframe itself?

3) How involved is BA/BA engineering in the specification of such FMCs, or is it 'standard' from the aircraft manufacturer (linked to Q1 above).
1.) Generically the FMC/Flight Management System started out life to assist with navigation of the aircraft. Years and years ago, the aircraft was navigated from radio waypoint to radio waypoint using fairly simple instruments in the cockpit. As inertial navigation systems become more sophisticated, aircraft could be navigated to predetermined latitude/longitude, aka waypoints. It then snowballed thereafter - lists of waypoints could be entered, diversions, lists of nearest airports, altitude constraints, standard departure/approach routes, company routes etc. Along with this functions got added on to calculate performance airspeeds (take-off/rotate, climb, cruise, landing speeds), engine power ratings, aircraft weight and balance management, etc. So to answer your question, it typically handles everything related to route planning, navigation, and aircraft performance management. Years ago the FMS was a standalone box (which connected to lots of other aircraft sensors and systems), whereas with modern aircraft it's much more of a central computer/app type architecture (non-federated).

2.) The whole thing is highly regulated - but what you tend to find is a PowerPC chipset or similar surrounded by some very high integrity hardware (qualified to extremes of pressure, temperature, vibration, power supply spikes/poor quality). The software level tends to run on something like Ada. The software validation process is huuuuuge, and is highly fault tolerant/resistant. It's quite variable, but you're probably looking at a 3 to 5 year development cycle from key requirements to certified system. The hardware development tends to be fairly incremental, with the clever work happening at the software level.

3.) This is really variable! Tends to be a given that the hardware is identical, but the changes occur at the software level. Some airlines are content to pick from a menu - so typically Boeing/Airbus et al will have some baseline packages available. More mature airlines will see value in specifying particular features that make their day-to-day business more efficient or safer. Truly bespoke features are v. v. expensive, so it tends to come down far more to user interface, menu structures, style of presentation etc. So for example, I used to work in business jets, and one particular customer wanted some features very specific to operations in to and out of Aspen. Rather expensive, but it gave them improved levels of safety and ability to get in during bad weather, for which they had a market edge.
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Old Feb 14, 17, 1:23 pm
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The certification requirements are very stringent from what I was told by a 747 captain at PHX years ago. He also said that the FMC runs on a 386 processor!
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Old Feb 18, 17, 2:09 pm
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A busy few days so I'm only just catching up with this thread. Thank you to all the contributors for their insight - as someone with an interest in both aviation and computing it is a fascinating area.
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Old Feb 18, 17, 3:04 pm
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Originally Posted by chucko View Post
The launch crews in the Minuteman III silos still decrypt their launch orders (please God no) using 8-inch floppies.
​​​​​​​makes sense, if you have to use them you have already lost.
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Old Feb 19, 17, 1:00 am
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Originally Posted by KARFA View Post
Ah of course, yes.

I think some airlines have gone to an electronic tech log? I may be completely wrong on this, I have some vague memory of seeing this somewhere.
Yup, even BA has eLog on the 787, but I think that it's a CAA/EASA requirement to get have a paper version as well...
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