jhooper
Posts: 5560
Joined: Thu Dec 13, 2001 8:27 pm

Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 2:34 am

I was wondering why the 777's backup ADI is glass rather than a physical instrument such as in the 767. Isn't the idea of a backup instrument to be as redundant is possible? By that logic, you shouldn't have both depend on electricity. I know people say that it's impossible to have a total electrical failure on the 777, but I'd never say "impossible".
Last year 1,944 New Yorkers saw something and said something.
 
N243NW
Posts: 1597
Joined: Thu Jul 24, 2003 4:29 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 2:39 am

I too realize that a total electrical system failure in a 777 is possible, but it is extremely unlikely. Plus, the electronic backups are probably more reliable than their mechanical counterparts anyway.
-N243NW Big grin
B-52s don't take off. They scare the ground away.
 
CPH-R
Posts: 6058
Joined: Thu May 03, 2001 5:19 pm

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 3:54 am

But still, an analogue instrument would still have a very hard time to break down, compared to a EADI

[Edited 2003-08-26 20:55:27]
 
cancidas
Posts: 3985
Joined: Thu Jul 03, 2003 7:34 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 4:13 am

they are requred by the FAA, i'm pretty sure.

i once got caught using a garmin gpsmap 196 inflight. when i talked with the pilots later they explained to me not only why it was taken away from me but also that electronic instrumentation does update quicker that the instruments on board the a/c. shocked, i tried it in my 172. sure enough, it did update faster and was more acurate than the anologs.
"...cannot the kingdom of salvation take me home."
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 5:01 am

I too realize that a total electrical system failure in a 777 is possible, but it is extremely unlikely. Plus, the electronic backups are probably more reliable than their mechanical counterparts anyway.

Correct, they are more reliable than a mechanical stby instrument. Don't forget a mechanical stby ADI also has a gyro in it so it too needs electrical power. LCD's consume less power than conventional instrument
 
dash8tech
Posts: 708
Joined: Mon Jul 05, 1999 8:40 pm

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 7:06 am

It probably (dash8tech, not 777tech) runs off of the battery bus and thus with a complete electrical failiure it's still running off the batts.
 
LSTC
Posts: 277
Joined: Sun Jun 01, 2003 11:45 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 10:34 am

But still, an analogue instrument would still have a very hard time to break down, compared to a EADI

This was the case not too long ago. Its taken a long time, but these electronic instruments have finally achieved a reliability level that makes them suitable as a standby instrument but with MTBF rates that are still slightly lower than many mechanical instruments.

FAR 25 requires that the loss of all sources of altitude or heading or attitude or airspeed must be extremely improbable. That includes the standby and main instruments. The term "extremely improbable" relates to a failure rate of 1x10E-09 per flight hour. So in many cases, to bring this failure rate to an acceptable level while using a less reliable electronic instrument, the main instruments may have to be a more robust (expensive) type or they may be a requirement to raise the redundancy. ie: 3 main altimeters instead of 2.

Of course the electronic standby instrument must be paired with a power supply that is independant of the aircraft generating system. This is usually in the form of a battery pack that is charged, but isolated from the main aircraft electrical system.

The battery packs must be capable of supplying power to the standby instruments for times varying from 30 minutes to a few hours depending on the operational approval sought.

It is interesting to note that the standby instruments must become operational with no flight crew action following a failure of the electrical system.

 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 12:24 pm

The B777, is of course different than most other airplanes. There is a SAARU (Secondary Attitude Air Data reference Unit) that contains the gyros and processes all of the information. It then sends this info to the Standby Attitude Indicator. The indicator is just a display...there is no gyro inside. The SAARU is powered by 28VDC. So in theory (as it has been said already), it is the same as other aircraft. You need 28VDC regardless.
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 3:57 pm

There are even certified aircraft with no backup instrumentation visible. The backups are built into the displays, driven directly and will pop up automagically if the normal instrumentation fails, of at the press of a button.

How you do it is secondary to showing that it can provide the demanded reliability and redundancy!

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
MD-11 forever
Posts: 550
Joined: Wed Mar 14, 2001 12:15 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 4:10 pm

The MD-11's operated by Swissair and later on Swiss also are equipped with a "glass backup instrument". The reason for this upgrade was the lesson learned from the SR111 accident. One finding was, that the position as well as the visibility of the standard backup instrumentation is not satisfying in case of smoke in the cockpit.

Cheers, Thomas
 
UTA_flyinghigh
Posts: 6304
Joined: Wed Oct 03, 2001 8:46 pm

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 5:35 pm

As you can see, even some classic 737's have glass backup instruments :
http://www.airliners.net/open.file/344388/L/
I don't know if that particular aircraft is an exception though.
Fly to live, live to fly - Air France/KLM Flying Blue Platinum, BMI Diamond Club Gold, Emirates Skywards
 
AJ
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 5:51 pm

The Boeing 747-400ER has also incorporated a LCD standby ADI (as well as the other electronic displays).

View Large View Medium
Click here for bigger photo!

Photo © Jason Milligan

 
LSTC
Posts: 277
Joined: Sun Jun 01, 2003 11:45 am

RE: Why Does 777 Have Glass "backup" ADI

Wed Aug 27, 2003 10:15 pm

FredT,

I'm curious. Is the "certified" aircraft you are talking about a FAR/JAR 25 aircraft or a GA aircraft?

I have a hard time believing you can meet the FAR/JAR 25 regulations with such a setup:

Sec. 25.1333

[Instrument systems.]

[For systems that operate the instruments required by Sec. 25.1303(b) which are located at each pilot's station--
(a) Means must be provided to connect the required instruments at the first pilot's station to operating systems which are independent of the operating systems at other flight crew stations, or other equipment.
(b) The equipment, systems, and installations must be designed so that one display of the information essential to the safety of flight which is provided by the instruments, including attitude, direction, airspeed, and altitude will remain available to the pilots, without additional crewmember action, after any single failure or combination of failures that is not shown to be extremely improbable; and
(c) Additional instruments, systems, or equipment may not be connected to the operating systems for the required instruments, unless provisions are made to ensure the continued normal functioning of the required instruments in the event of any malfunction of the additional instruments, systems, or equipment which is not shown to be extremely improbable.]


 
CX Flyboy
Posts: 6007
Joined: Sun Dec 26, 1999 6:10 pm

RE: Why Does 777 Have Glass "backup" ADI

Fri Aug 29, 2003 10:44 pm

In our 777s we have two standby instruments, one AH, and the ASI. The 777-300ER aparently has one single intergrated standby instrument just like a mini PFD, and we are considering having this retrofitted to our current 777s.
 
s.p.a.s.
Posts: 916
Joined: Sun Mar 11, 2001 2:04 pm

RE: Why Does 777 Have Glass "backup" ADI

Fri Aug 29, 2003 11:01 pm

Speaking about the backup ADI from the MD11, I made this same question to a friend who happens to be a F/O with Swiss and he told me that indeed it provides better reading and also no parallax errors.. About power source, he told me that it is connected to the INS 2 battery and to the plane's battery bus.

Lufti(LH) is also installing those to their MD11's and perhaps it will be standard retrofit from now on for another MD11s around.

Rgds

Renato
"ad astra per aspera"
 
User avatar
Crosswind
Posts: 2536
Joined: Sat Nov 25, 2000 4:34 am

RE: Why Does 777 Have Glass "backup" ADI

Sat Aug 30, 2003 5:58 am

Newer B757s (so I would assume this also applies to 767s) have an electronic standby ADI. It appears to be an option on any new-build Boeing aircraft...

Regards
CROSSWIND

Who is online

Users browsing this forum: No registered users and 20 guests