Section Meeting Report
by Gary Louie, PNW Secretary
May 10, 2000

Design of the Audio Management Unit for the Boeing 777 Aircraft
Chuck Kettle, Avtech Corporation

The PNW section held its May meeting at Jack Straw Studios in Seattle. Avtech engineer Chuck Kettle brought his PowerPoint slides and many pieces of aircraft panel hardware to describe the Audio Management Unit (AMU) for the Boeing 777 aircraft.

Avtech is a Seattle aviation engineering firm that began in 1953 by selling aircraft jack panels. Today it has 350 employees and makes almost anything for aviation - such as power supplies, harmonic filters, lights, and audio equipment.

He passed around a panel for the 777 AMU, which has various switches and knobs for selecting and controlling cockpit audio. He also passed out several other control panels and bits of aircraft hardware.

As many as four people in the cockpit need to be able to select between 3 mics (a hand mic, boom mic and a mic in their emergency oxygen mask) and be able to route to any of the radios, intercoms or PA system. Noise cancelling mics are used in all cases. An audio panel functions like a mixer for each listener - they can select several things to listen to and their volumes. Oddly, one of the biggest problems is pilots sitting on their hand mics without knowing it. This activates the mic and occupies a radio channel, denying use to anybody else. Their ACU times the use and sends a warning if activated too long.

The system makes extensive use of DSP and microprocessor control, interfacing with the airplane, which is also "fly by wire", or all-computer controlled. He described the ARINC 629 interface (Aeronautical Radio Inc) which is like a LAN (local area network).

Lots of analog audio is still going around the circuits, though, and airplane power is 400 Hz so power supply interference can be plainly audible. Careful attention must be paid to grounding and shielding, just like in a recording studio.

A question was asked about needing to turn off consumer electronics in the plane. Most consumer stuff puts out a lot of electronic noise, so to be careful, airlines have you turn them off. Anecdotal stories were given about airplane instruments being affected by such devices.

Chuck showed a PA amplifier they developed that is setup and calibrated by attaching a laptop computer, eliminating the need for adjusting pots manually.

As an example of little details that count, Chuck related the story behind designing a simple way to hold the intercom handset into the cradle. It turned out that something like a magnetic cabinet latch worked. But they had to find a vendor that could supply an aircraft quality unit, at some expense. It was tricky to find a unit that would have just the right amount of holding power. Finding a decent cable and strain relief was also tricky.

Chuck showed many slides of Avtech's design, production and testing facilities, such as the EMI (electromagnetic interference) test chamber, shake table and heat/cool chamber. Products must be thoroughly stressed before use.

The construction of the certified aircraft hardware was very interesting, and a far cry from consumer electronics.

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Last modified 11/4/2001.