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convair880mfan
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Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 2:55 am

I've seen quite a few videos on how commercial airplane manufacturers test various structures for stress tolerance. Are avionics also tested? Seems like in severe turbulence these complex and sensitive instruments would take quite a beating internally.

There are few videos where a narrator tours the avionics compartment of an airliner. I remember seeing massive bundles of wires. I imagine the connectors are pretty robust as are the things that secure various components. But what about the innards of these instruments? Do G loads affect them?
 
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Aaron747
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 2:57 am

convair880mfan wrote:
I've seen quite a few videos on how commercial airplane manufacturers test various structures for stress tolerance. Are avionics also tested? Seems like in severe turbulence these complex and sensitive instruments would take quite a beating internally.

There are few videos where a narrator tours the avionics compartment of an airliner. I remember seeing massive bundles of wires. I imagine the connectors are pretty robust as are the things that secure various components. But what about the innards of these instruments? Do G loads affect them?


They will not take a beating if properly secured. Think about it. Have you looked at a motherboard before? Everything is fixed or soldered in place.
 
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Starlionblue
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 3:00 am

All the stuff down there is quite rugged and bolted down or strapped down neatly.

The innards of modern instruments aren't really that sensitive. They're solid state so nothing to shake loose really. Not even gyros have moving parts nowadays. For that matter, older instruments which do have moving bits have been used for many decades in fighter and aerobatic aircraft.
 
GalaxyFlyer
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 3:27 am

The old gyros in fighters withstood hundreds of 7+ g loads. The stuff is pretty rugged. Same in transport category. Turbulence doesn’t put that much G loading anyway, rarely even 2 g.
 
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fr8mech
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 10:43 am

In 30+ years of aircraft maintenance I can’t recall a single incident of “when in turbulence my ‘x’ was erratic” or “after turbulence the ‘x’ was inoperative”.

Wiring is secured. Boxes are locked down. Racks and panels are robust and secured to the airframe. Connectors have a positive lock.

Do things, usually connectors, come loose? Yes, but that is usually a worn connector or a connector that wasn't properly installed.
 
extender
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 4:30 pm

Some LRU racks have shock mounts, but it has been a while since I crawled in an E&E.
 
kalvado
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 5:33 pm

As a general concept - planes should be designed to withstand common operation conditions and then some. Turbulence is an expected condition, so nothing should fail there. Wing load tests are spectacular and well published; electronics tests are less so - but they do exist.
Some video to give a general idea of testing: https://www.youtube.com/watch?v=I4Jcf3YbaoA
How that is achieved is a whole different story. A lot of work to make it happen...
 
Flow2706
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 9:17 pm

There was one case where a bleed air duct detached during a severe turbulence encounter. However, it was determined that the connector was not secured correctly to beginn with and it would have shaken loose anyway, possibly a bit later: http://www.bst-tsb.gc.ca/eng/rapports-r ... 5f0165.pdf However, as mentioned by other posters it's highly unlikely that equipment fails solely because of turbulence. I once experienced a downgrade in auto landing capability (from CATIII Dual to CAT III Single) over southern Spain in (solid) moderate turbulence. However this is not a system failure, but "normal system behavior" caused by momentary disagreement between two ADRs (as the probes are positioned in different positions on the forward fuselage a momentary yaw moment due to turbulence could cause a difference between two of them). If two ADRs disagree, the auto land capability automatically downgrades for the rest of the flight.
 
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fr8mech
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Re: Can severe turbulence damage avionics in the E&E bay?

Tue Aug 03, 2021 9:19 pm

Flow2706 wrote:
There was one case where a bleed air duct detached during a severe turbulence encounter. However, it was determined that the connector was not secured correctly to beginn with and it would have shaken loose anyway, possibly a bit later: http://www.bst-tsb.gc.ca/eng/rapports-r ... 5f0165.pdf However, as mentioned by other posters it's highly unlikely that equipment fails solely because of turbulence. I once experienced a downgrade in auto landing capability (from CATIII Dual to CAT III Single) over southern Spain in (solid) moderate turbulence. However this is not a system failure, but "normal system behavior" caused by momentary disagreement between two ADRs (as the probes are positioned in different positions on the forward fuselage a momentary yaw moment due to turbulence could cause a difference between two of them). If two ADRs disagree, the auto land capability automatically downgrades for the rest of the flight.



Ha, I would’ve sworn that was a B767 when I read your post. Damn ducts in the fwd pit, left sidewall are always separating at the coupling.
 
Weatherwatcher1
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Re: Can severe turbulence damage avionics in the E&E bay?

Thu Aug 05, 2021 1:29 pm

Stress analysis is done on all components including avionics to ensure they are capable of withstanding maximum G loads as well as vibration. Components are actually tested on shaker tables as a part of their certification to ensure they can withstand the vibration experienced over the life of an airplane. As airplanes age, physical degradation from vibration often is what leads to failure. 20 year old connectors, pins, wiring, etc degrade which leads to intermittent failures.
 
celestar345
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Re: Can severe turbulence damage avionics in the E&E bay?

Fri Aug 06, 2021 3:17 am

fr8mech wrote:
Ha, I would’ve sworn that was a B767 when I read your post. Damn ducts in the fwd pit, left sidewall are always separating at the coupling.


Which duct? There are so many ducts around that area.... and on older 767 the amount of tape repair on the ducts are just beyond belief.....
 
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fr8mech
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Re: Can severe turbulence damage avionics in the E&E bay?

Fri Aug 06, 2021 7:23 pm

celestar345 wrote:

Which duct? There are so many ducts around that area.... and on older 767 the amount of tape repair on the ducts are just beyond belief.....


Flight deck conditioned air. When I get back to work next week, I’ll see if I can dig up its actual nomenclature and the station number where the separation occurs.

By the way, that problem has nothing to do with turbulence. It’s a Pack temp control issue. The pack out air get so cold that ice crystals form and cause a back pressure. Enough of a back pressure and the duct separates at the joint/sleeve.

But, anytime we get a write up that says flow to the flight deck is low…we send the guys right there. We want them to gain access as quickly as possible and see if there is any evidence of ice formation.
 
SMYD
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Re: Can severe turbulence damage avionics in the E&E bay?

Sat Aug 07, 2021 5:19 pm

The only examples I can think of are the main batteries of certain A320 aircraft. The severe turbulence inspection calls for examining the battery hold down rods. There have been instances where they have broken.

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