B777 AIMS Display System

[B777EFIS]

I worked for Boeing from 1987 to 1995 on the development of the LCD displays that are used in the 777 flight deck. Someone pointed me to this forum and suggested that people here might be interested in learning more about how the B777 Display system and the AIMS system work. I am offering to answer questions relating to the B777 displays if anyone is interested.

[18Wheeler]

I hear that the early experiments with a Windows based OS weren't very successful ...

http://www.onthenet.com.au/~billzila/777death.jpg

Just kidding .... :)

Looks like a nice flgiht deck - certainly bigger than the 747.

[This message has been edited by 18Wheeler (edited 16 January 2001).]

[B777EFIS]

LOL! A pilot who knows how to use photoshop!

[18Wheeler]

Nah, I actually copied off here somewhere.
FWIW, the only time I've come close to being in a 777 cockpit was when I as doing some training in Denver Colorado in 1994, and United had just gotten delivery of their brand new 777 simulator. It came in three blue boxes - BIIIIGGGG blue boxes, on an AN-124.
The day before I left, the engineers had the bare cockpit sitting on the ground so I walked in and had a look. Don't remember much, it seemed like it had a fair amount of room.
Not enough engines, though. ;)

[Luftwaffle]

I don't want this interesting offer of free technical information to go to waste, so I'll ask a question.

I don't have any glass cockpit experience or training whatsoever, so this question isn't specific to the B777, but it's to get the ball rolling.

The digital data displayed on the screens is based on initial analogue data, such as raw pitot pressure and static pressure. At what point, and how is the information digitized? That is, is the pressure at each pitot and static source immediately converted to a number via a digital barometer, and then numerically compared to determine IAS, or is there an underlying "steam-driven" ASI, altimeter, etcetera, working with anaroid capsules? By what logic are the redundant pitot and static pressures compared?

[B777EFIS]

I can't speak for all airplanes, but on the 777 the Air Data Module pitot and static ports had built-in transducers and analog to digital converters that output digital data on dedicated ARINC 429 and on the ARINC 629 Flight Controls Bus to AIMS (Airplane Information Management System) through redundant I/O modules in the AIMS cabinet, and that data was then processed by the displays function for display on the screens, and made available to the FMS and other functions that needed it.

The standby instruments receive direct ARINC 429 inputs from backup pitot and static sensors. The standby instruments are also LCD's, and they can be powered from the battery bus if all other power is lost.

The input air data is processed by the AIMS display system before display. I don't recall the specifics, but I know there was a validation and source selection algorithm, and there are manual source selection switches on the main panel below each ND.

[Coffins Corner]

Its reasonable to assume there are multiple data buses (redundant) on 777, right?

My question is more on how 429 standard works (I misplaced the grey-cover a long time ago)...as I understand it, you have one main data bus on which all talkers transmit in 32-bit(?) words with something like a 6-bit label.

Now, would I be correct in assuming the AIMS cabinet is one of the few listeners, or is it common for other systems to not have their data relayed through the AIMS? I deal with crash recorders and QARs (so I have virtually no idea of how *modern* comm. standards work). Do you know if the AIMS also performs the function of compiling and formatting the data for the recording systems?

Maybe an answer would be more succinct if I asked, "What doesn't the AIMS do?"

:)

[Dr. Red]

A more trivial question: what's the expected system failure rate?

i.e. does Boeing specify the system "will fail in less than 1/1000000 flights" - or do you not bother with this sort of probability?

[B777EFIS]

Regarding the ARINC 429 data standard, there is only one talker per bus, and many listeners. AIMS acts as a data conversion gateway for a good deal of the data on the 777, and is the core of the 777 avionics. There are redundant 429 busses in some cases, but often only one per device (talker). ARINC 629 is a many talker, many listener bus that is like an ethernet LAN in a way. There are 3 main ARINC 626 busses on the 777, the Flight Controls, Systems, and AIMS Intercabinet busses. The flight controls bus consists of 3 separate sub-busses (twisted pairs), while the Systems and AIMS busses each have 4 twisted pairs (for redundancy).

Critical system failure rates are typically designed for 1E-9 per flight hour.

[Pegasus912]

Did you not consider using fibre optic data buses rather than twisted pair? Fibre would seem to have obvious advantages; higher bandwidth, immunity to outside interference, lightweight...

[B777EFIS]

Fiber optics busses were considered for the 777, and were used for the non-critical Avionics LAN. Fiber optics were rejected for the critical systems busses for several reasons.

There was not enough in-flight test data for fiber optics.

Fiber optics require special connectors, and a greater deal of skill to splice when they break than wires do. This was cause for concern in terms of maintainability in the field, and overall reliability.