Guest

717 - No Mechanical Backup Instruments?

Wed Jul 25, 2001 6:58 am

Hey guys,

I was watching that 717 flightdeck shot the other day when I realized that there was no basic mechanical instruments (Airspeed Indicator, Altimeter and Attitude Indicator) that could be used as a back up in case of electrical failure. I'm pretty sure that electrical systems are redundant and that you'd probably have better odds at winning the lotery rather than having a full blown electrical failure, but some people do win the loteries, and electrical failure happens.

So my question is, is there is mechanical instrumentation on the 717? If no what would one would do in case of an electrical failure on the 717 with IMC conditions?


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Regards,
Nicolas
 
XXXX10
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RE: 717 - No Mechanical Backup Instruments?

Wed Jul 25, 2001 7:59 am

I may be wrong but looking closely at the bac up instruments on the747/777 they seem to be electrical as well, maybe this has something to do with it
 
Guest

RE: 717 - No Mechanical Backup Instruments?

Wed Jul 25, 2001 9:09 am

Aren't the backup systems on these aircraft driven by the vacuum pump and the pitot tubes? Well expect for the Attitude Indicator which is driven by electric gyros.

Regards,
Nicolas
 
seagull
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RE: 717 - No Mechanical Backup Instruments?

Wed Jul 25, 2001 1:41 pm

No vacuum pump in a jet. The third attitude indicator is electrically powered off the battery bus in all of the aircraft I am familiar with. The standby airspeed/altimeter are similarly powered, although some aircraft types may have their own dedicated battery.
 
Guest

RE: 717 - No Mechanical Backup Instruments?

Wed Jul 25, 2001 2:34 pm

What I do know is that the backup instruments for the 777's LCD's are just more LCD's.
 
modesto2
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RE: 717 - No Mechanical Backup Instruments?

Wed Jul 25, 2001 11:53 pm

Just a point of clarification: the 777 and 717 do not have clock-style back-up instruments, but the 747 and 764 have clock-style back-up instruments.
 
FDXmech
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RE: 717 - No Mechanical Backup Instruments?

Thu Jul 26, 2001 4:49 am

A very good observation.
Just understand, whether the standby attitude indicator is mechanical or an LCD type, it requires electrical power to operate.

On the other hand, traditional standby altimeter/airspeed indicators (this includes the MD11) do not require power (other than the integral light and altimeter vibrator) to function, just a pitot/static source.
So perhaps the regulations were modified in that a backup altimeter/airspeed indicator (LCD type) now allow a power source to operate it.
You're only as good as your last departure.
 
JETPILOT
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RE: 717 - No Mechanical Backup Instruments?

Thu Jul 26, 2001 8:14 am

The Standby attitude indicator isnt powered off the same bus as the FO/CA attitude indiators. It has its own indipendant power source (usually the aircrarft batery on the STBY bus). So unless the battery goes dead then you'll have electrical power to run the STBY attitude indicator for a minimum of 25 minutes.

The STBY bus is indipendant of all other busses. So failure of all other buses will have no effect on the STBY attitude indicator.

Operation of the STBY bus is checked before every flight by isolating it from the other bussses and running it off the battery simulating loss of all generators.

So weather its mechanical or not....it will still be powered.

The chances of losing all your busses including the STBY bus are astronomical.

The proper terminology for a mechanical type instrument is an anologue indicator....or in the biz its a "steam guage".

JET
 
Pilot1113
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RE: 717 - No Mechanical Backup Instruments?

Thu Jul 26, 2001 9:27 am

A 717 did suffer a total electrical power failure upon take off a few years ago.

As I believe, an AirTran 717 suffered a loss of all electrical components. As it was VFR, they went around and landed uneventfully.

- Neil Harrison
 
critter
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RE: 717 - No Mechanical Backup Instruments?

Thu Jul 26, 2001 9:58 am

The B717 not only has a backup buss for its instrumantation but some essential instruments have their own backup battery that will supply power for a minimum time if required. I am only giving you a general outline.........I'm sorry I don't feel like pulling out all of my books and diagrams at this time.

The total electrical failure that Neil is talking about was actually not a total failure but a loss of indication from the six large LCD's, all are powered by two Versitial Integrated Avionics (VIA) units. There apperently was an chance that both could loose power under a particular condition. Changes have since been made so that should not happen again. In that instance however, the crew still maintained use of the ISIS or Integrated Standby Instrument System, which provided all of the pertenant information for the crew. The ISIS is located in the fwd center pedestal.

P.S. There is only one Mechanical "clock type" gauge in the cockpit.........Can you name it!!!!!!!!!

I will check back to tell you if you are correct.


critter
 
DG_pilot
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RE: 717 - No Mechanical Backup Instruments?

Fri Jul 27, 2001 1:03 am

Does the magnetic compass count?
 
b767-400er
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RE: 717 - No Mechanical Backup Instruments?

Fri Jul 27, 2001 5:25 am

Stand-by ADI in front of throttles?

Tony,
B767-400er
 
wannabe
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RE: 717 - No Mechanical Backup Instruments?

Fri Jul 27, 2001 7:27 am

The Mickey Mouse watch on the pilots wrist?
 
Guest

RE: 717 - No Mechanical Backup Instruments?

Mon Jul 30, 2001 8:28 am

Is it the little flight number mechanical thing under the glare shield?
 
XFSUgimpLB41X
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RE: 717 - No Mechanical Backup Instruments?

Mon Jul 30, 2001 9:18 am

That ADI is an EADI.... so it's not a standard one.. still a graphic LCD display. The radios and transponder are the only ones that look like a normal standard system to me-- so im gonna also have to go with the Mickey Mouse watch on the copilot's wrist.
Chicks dig winglets.
 
AA737-823
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RE: 717 - No Mechanical Backup Instruments?

Mon Jul 30, 2001 12:32 pm

I believe both AirTran AND TWA had a couple of 717 electrical failures. It was due to condensation dripping into the computer system- both computers failed due to short ciruit. It happened immediately after the wheels came up, IIRC.

Randy
 
Guest

RE: 717 - No Mechanical Backup Instruments?

Mon Jul 30, 2001 2:04 pm

there ARE backups! look closely behind the throttle!
 
242
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RE: 717 - No Mechanical Backup Instruments?

Mon Jul 30, 2001 3:28 pm

>>>P.S. There is only one Mechanical "clock type" gauge in the cockpit.........Can you name it!!!!!!!!! <<<

>>>I will check back to tell you if you are correct. <<<

My memory is a little fuzzy, but I'm pretty sure there's an O2 gauge at the top of the overhead panel.

Oh, Airtrans little incident with ship 706 was caused by water leaking from a poorly designed fwd galley ice bin drain. It ended up dropping on the r/h BPCU (Bus Power Control Unit) and caused five of the six displays to go blank among other things.

Has Airtran installed catch pans above the equipment in the A/E bay to prevent future problems?


 
critter
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RE: 717 - No Mechanical Backup Instruments?

Tue Jul 31, 2001 4:21 am

242, You are correct. There is a little o2 gauge on the top of the overhead panel that is still a dial type. That is the only mechanical gauge in the cockpit other than the standby compass that someone mentioned. I doubt you will find any pictures of the compass however because it is were all stby compasses are on any DC-9 or MD-80, up behind the first officers head.

For those of you who mentioned the radio's. Everything on the B717 is digital. In fact other than the above mentioned o2 gauge, i believe the only other dial type gauges you will find on the aircraft are the pressure gauges mounted on the hyd system accumulators and the oxygen and fire bottles.

And yes the electrical failure was a result of condensation dripping down into the E&E compt. That is something that Boeing has fixed on all B717 and is now a part of the manufacturing process. So like I said, that should not happen again!!!!!

critter

 
critter
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RE: 717 - No Mechanical Backup Instruments?

Tue Jul 31, 2001 4:43 am

Here is a picture of your one and lonely gauge.


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Photo © Frank Schaefer





critter
 
174thfwff
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RE: 717 - No Mechanical Backup Instruments?

Tue Jul 31, 2001 12:59 pm

What about the ram air system? Does this provide any help if the battery fails?

Or is the ram air for other systems?
Brooklyn, Queens, Manhattan, Staten, Uptown, what now? Lets make it happen.
 
critter
Posts: 258
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RE: 717 - No Mechanical Backup Instruments?

Wed Aug 01, 2001 4:26 am

This aircraft does not utilize a Ram Air Turbine (RAT). The only ram air useage is for cooling of the brakes in the wheel wells, and cooling of the conditioned air through heat exchangers in the tail.

critter

 
Guest

RE: 717 - No Mechanical Backup Instruments?

Wed Aug 08, 2001 6:54 am

A few all electric standby instruments have been allowed by the FAA (777 being the other one). CFR (code of federal regulations) 121.305 requires (part 121) aircraft 30 minutes of reliable operation from a power source, independent of the electrical generation system, for the third attitude instrument.

I believe that the FAA is more conservative than that in practice, a recent guidance memo stipulates that for an all-electric backup to be used it has to work for 60 minutes and more for ETOPS aircraft. No doubt the 717 standby meets this 60 minute "requirement".

Regards,
Nut
 
AAR90
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RE: 717 - No Mechanical Backup Instruments?

Wed Aug 08, 2001 10:48 am

AA's 737-800s will be upgrading to a single combined electronic stand-by instrument display to replace the mechanical stand-by instruments of today. Probably will be a couple of years before all planes are modified.
*NO CARRIER* -- A Naval Aviator's worst nightmare!

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