777 MCP Altitude Window Changing Without Pilot Action
 

Remember that Boeing Bulletin.... 'To inform flight crews that the altitude in the MCP altitude window may change indication without pilot action'? Never personally saw it happen but according to the bulletin..... 'An operator has experienced multiple occurrences of the MCP altitude window indication changing by 1000, 1500, 2000, and 4000 foot increments during climb, cruise, and descent. These changes occurred without flight crew input to the MCP. In addition when operating in VNAV, the altitude indication has changed after the altitude selector was pushed.'

Then the bulletin said...."Initial findings suggest that electrostatic discharge introduced when the pilots touch the MCP may be causing the value in the altitude window to change."

But when I attended a Boeing symposium, if I understood correctly, they said that they were leaning toward the theory that it was caused by the occasional random cosmic ray. Imagine that...a random highly charged atomic particle passing through the airplane and possibly leading to an altitude violation.

Yep, I know the bulletin but I hadn't heard that specific theory..I thought there was a theory/grade A rumour doing the rounds that the problem might be caused by static discharge from the gloves some flight crew were in the habit of wearing....I guess a cosmic ray might well produce a similar effect.

I think the (unknown) operator in question is trying cover up a multiple level-violator past mistakes.

Maybe a BBJ?

In 18 years, 13,000 hours and with biggest operator of the type, and every variant, l have never heard anyone saying they have seen this phenomena, let alone witnessing it myself.

halas

The 787 TCP (radio tuning panel) had a similar issue where the active frequency was changing to standby by itself

I had this happen to me on a 787. Coasting in eastbound, changing from Shanwick to Shannon at FL410. ATC gave me a squawk and then asked to confirm our level. I replied “410”, having glanced at the altimeter. “Check your MCP” came the reply. It was set to 50,000ft. Neither of us had touched the altitude selector since the last climb to FL410. No turbulence, lightning, St Elmo’s fire, etc. No-one wearing gloves. We re-set 41,000, made an entry in the e-log, filed an ASR and went back to the crossword.

The original post was about a bulletin in the B777 FCOM

Dreamliner may have more of an issue, but l don't know.

Any comments from 74-8 operators?

halas

First observed on a B737-300, the one with the new MCP. In the same time frame, it was observed on a B767. It did lead to a loss of separation incident with a QF 747 and a AN B737 climbing out of Adelaide.

The advice then was from Boeing to keep checking the MCP selected ALT. They had no idea why it was happening. The theory was electrostatic discharge from pilots fingers because we sat on proper sheepskin seatcovers, but wore nylon wool mix trousers with rubber soled shoes. Seemes plausible.

And it was 1986, so Boeing has known about it for a long time. It was a new B777 Manager at Boeing, with a great deal of experience on the B737, who caused the Bulletin to be written.

Oh, and I did see the MCP ALT change without pilot input while working for AN, but never on the B777.

The important phrase is "when MCP selections are complete, select 1000." Use common sense and it is no big deal.

If equipment was susceptible to cosmic rays, then any and all data in the aircraft could be randomly corrupted, which would cause chaos.

This is far more likely to be caused by electrical interference on the data lines, or power supply lines, originating from the aircraft itself.

PS, can you explain the "select 1000" Three Wire?, I have not flown 777/787. What do you have to do operationally?

Maybe they mean to put the selector switch from “hundreds” back to “thousands”?

This is not asked for in the 787 bulletin. It merely states (inter alia): “If this occurs, verify the last cleared altitude, set the correct altitude on the MCP, and ensure that the correct pitch mode is selected.
There is no action the crew can take to cause or prevent this anomaly.”

There is a rotary selector switch with two selections: auto - 1000.
auto is used when flying a VNV approach, otherwise thousands for where airplanes fly normally.

Never seen it on a B748, yet.

:ok:

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Changing by consistent fixed values or just random? Yikes!

I have experienced this first hand, it’s startling. Not only the altitude window changed by 4000’ or so the MCP hdg changed by 90 odd degrees as well. There was no consequent flight path change as we were LNAV & VNAV PTH maintaining assigned level. This happ when I was aligning the hdg bug in cruise and I def felt there was some static. And I don’t wear gloves or caps or helmets etc...