Royal Nepal 757
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Faire d'income
Triple IRS failure will cause loss of both EADIs, EHSIs, RMDIs, IVSIs and all equipment fed by IRS. (FCCs, TMC etc). All alternate flight instrument selections, other than alternate air data, would also be useless. You are down to standby instruments.
It would be interesting to know how all three failed (if indeed they did).
Triple IRS failure will cause loss of both EADIs, EHSIs, RMDIs, IVSIs and all equipment fed by IRS. (FCCs, TMC etc). All alternate flight instrument selections, other than alternate air data, would also be useless. You are down to standby instruments.
It would be interesting to know how all three failed (if indeed they did).
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I would recommend reposting some of these messages on the Tech Forum, but be prepared for more "utter tosh" comments. I'd especially like to hear the reaction to Dagger Dirk's message 
Re RDMI...
The DME, at least, should have been working on the RDMI's (with manual VOR tuning).
Re TOGA
Pushing the TOGA switch doesn't do anything to the IRS's. Only the FMC position is affected (where GPS is not a valid FMC input).
Re Antiskid
Antiskid does not equal Autobrake (two different things... although the Autobrake is dependent on a functioning A/S system.... and a functioning IRS system (unless we're talking RTO)).
If the 757 is like the 767, the Antiskid system only needs the IRS's for hydroplane/touchdown protection. I'd wager that the other antiskid functions would be ok (allowing normal manual braking with antiskid protection for the rest of the rollout).
Re triple IRS failure
It's not unheard of, but flight crew error has been the cause on at least one occasion (quick realignment at the threshold + takeoff roll started too early). I wonder if they tried ATTitude mode after they lost their displays? (This would have given them attitude and, if they entered a valid heading, VOR and perhaps a fully functioning ILS display).
Regards.
Q.
Re RDMI...
The DME, at least, should have been working on the RDMI's (with manual VOR tuning).
Re TOGA
Pushing the TOGA switch doesn't do anything to the IRS's. Only the FMC position is affected (where GPS is not a valid FMC input).
Re Antiskid
Antiskid does not equal Autobrake (two different things... although the Autobrake is dependent on a functioning A/S system.... and a functioning IRS system (unless we're talking RTO)).
If the 757 is like the 767, the Antiskid system only needs the IRS's for hydroplane/touchdown protection. I'd wager that the other antiskid functions would be ok (allowing normal manual braking with antiskid protection for the rest of the rollout).
Re triple IRS failure
It's not unheard of, but flight crew error has been the cause on at least one occasion (quick realignment at the threshold + takeoff roll started too early). I wonder if they tried ATTitude mode after they lost their displays? (This would have given them attitude and, if they entered a valid heading, VOR and perhaps a fully functioning ILS display).
Regards.
Q.
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Q
IRS:
Agreed to all your tchnical details. The airlines in question never does quick aligning of irs, Boeing taught them to do only full align. Therefore slim chance of crew inadvertently leaving irs in align mode. The 757 of RNAC has no gps backup.
RDMI:
Yes, manual tuning of vor NO 1 gives needle pointing to the staion but without HDG information, since heading info is derived from irs.They do not practice std by (only) instrument approach during PC.Besides, it is a VOR/DME 15mile arc approach for RWY 02 in KTM.
Yes, Auto brake does not function without A/S of Normal brake (R-sys). However, A/S functions normaly on ALT Brake (L-sys) and also RSV Brakes.
IRS:
Agreed to all your tchnical details. The airlines in question never does quick aligning of irs, Boeing taught them to do only full align. Therefore slim chance of crew inadvertently leaving irs in align mode. The 757 of RNAC has no gps backup.
RDMI:
Yes, manual tuning of vor NO 1 gives needle pointing to the staion but without HDG information, since heading info is derived from irs.They do not practice std by (only) instrument approach during PC.Besides, it is a VOR/DME 15mile arc approach for RWY 02 in KTM.
Yes, Auto brake does not function without A/S of Normal brake (R-sys). However, A/S functions normaly on ALT Brake (L-sys) and also RSV Brakes.
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Well,
Away for a few days and it seems I have a new handle (the mouth), nice ring to it.
For Overtalk,
My qualifications are my concern, but for your info I am a UK qualified licenced engineer, both CAA and JAA with 757 A/B2/C type rating on my licence, which I have held since '87. I am also an incorporated engineer and a member of the RAeS.
From August '97 to March 98, I was employed at RNAC by a western 3rd party maintenance organisation to oversee the line maintenance at KTM on RNAC's B757's (the company had been contracted to carry the maintenance for RNAC, both line and hangar).
When I have more time to write I may say a little more about my experiences at RNAC, Indeed I may speculate a little more about the possible causes of the triple IRS failure.
For now I will say this. I suspect the IRS failure may have been down to poor racking. I recall replacing an IRU at RNAC which required some force to correctly rack. It may be that others were equally difficult to rack resulting in poor pin contact which became apparent as T/O power was applied. This may provide some clue as to why the crew did not, or were not able to, select ATT to restore at least horizontal and directional information to the EHSI and EADI, as I am sure this would be a QRH action (I don't have a QRH to hand to verify)
This scenario may also explain why at first there was only one U/S IRU, then all 3, then back to just one, as some re-racking may have taken place to attempt to restore servicability and perhaps move a U/S IRU from the left side to another position to restore GPWS data (IRU is hard wired not switched into the GPWC, so a U/S IRU can mean certain GPWS terrain envelope modification is not enabled).I cannot say more than this as I don't know enough information as to the current RNAC a/c mod state.
Qavion, You are of course right, TOGA press sets the datum for FMGC PPOS (runway threashold). The 757 anti-skid is identical in operation to the 76 with the exception that the normal a/skid uses the right system not the centre.
Hope this clarifies things.
Cheers,
Mono (the mouth)
Away for a few days and it seems I have a new handle (the mouth), nice ring to it.
For Overtalk,
My qualifications are my concern, but for your info I am a UK qualified licenced engineer, both CAA and JAA with 757 A/B2/C type rating on my licence, which I have held since '87. I am also an incorporated engineer and a member of the RAeS.
From August '97 to March 98, I was employed at RNAC by a western 3rd party maintenance organisation to oversee the line maintenance at KTM on RNAC's B757's (the company had been contracted to carry the maintenance for RNAC, both line and hangar).
When I have more time to write I may say a little more about my experiences at RNAC, Indeed I may speculate a little more about the possible causes of the triple IRS failure.
For now I will say this. I suspect the IRS failure may have been down to poor racking. I recall replacing an IRU at RNAC which required some force to correctly rack. It may be that others were equally difficult to rack resulting in poor pin contact which became apparent as T/O power was applied. This may provide some clue as to why the crew did not, or were not able to, select ATT to restore at least horizontal and directional information to the EHSI and EADI, as I am sure this would be a QRH action (I don't have a QRH to hand to verify)
This scenario may also explain why at first there was only one U/S IRU, then all 3, then back to just one, as some re-racking may have taken place to attempt to restore servicability and perhaps move a U/S IRU from the left side to another position to restore GPWS data (IRU is hard wired not switched into the GPWC, so a U/S IRU can mean certain GPWS terrain envelope modification is not enabled).I cannot say more than this as I don't know enough information as to the current RNAC a/c mod state.
Qavion, You are of course right, TOGA press sets the datum for FMGC PPOS (runway threashold). The 757 anti-skid is identical in operation to the 76 with the exception that the normal a/skid uses the right system not the centre.
Hope this clarifies things.
Cheers,
Mono (the mouth)
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royal nepal
"Most unusual things happening is uasual in this country.
It is unusual to appoint a F/O as operations director. But it is usual in Nepal, when relations with minister is strengthened by donation.The said ops director was jailed on charges of forgery for smugling ilegal immigrants to Japan.
Second in line in ops for international ,landed at Delhi without landing clearence on wrong runway. Doctors should monitor more seriously this guys health since he is overweight,suspected of sugar problem. I think this is the begining of the end for this company. Professionals are overrun by unprofessionals.It is duty of Every responsible person to protect life of innocents on board and ground. Passengers will think twice before buying tickets."
Agree 100% with middle path on "begining of the end for this company". Having known how poor their maintainence is, the qualifications of senior staffs and flight punctuality, I do not prefer travelling with them unless I have no other choice. Thats my personal opinion.
It is unusual to appoint a F/O as operations director. But it is usual in Nepal, when relations with minister is strengthened by donation.The said ops director was jailed on charges of forgery for smugling ilegal immigrants to Japan.
Second in line in ops for international ,landed at Delhi without landing clearence on wrong runway. Doctors should monitor more seriously this guys health since he is overweight,suspected of sugar problem. I think this is the begining of the end for this company. Professionals are overrun by unprofessionals.It is duty of Every responsible person to protect life of innocents on board and ground. Passengers will think twice before buying tickets."
Agree 100% with middle path on "begining of the end for this company". Having known how poor their maintainence is, the qualifications of senior staffs and flight punctuality, I do not prefer travelling with them unless I have no other choice. Thats my personal opinion.
Last edited by PPRuNe Towers; 20th Oct 2003 at 14:14.
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Ah, but what REALLY happend?
This thread is a grand example of uninformed speculation. Some of the posts are outrageous to say the least and many more are downright defamatory, but at no time has there been an accurate statement of the actual symptoms of the original defect, nor of the procedures that were then followed by the RNAC engineers before they raised an ADD on the centre IRS.
Just to keep the pot boiling, perhaps the experts here may wish to discuss among themselves what happens if incorrect longitude coordinates are entered into the IRS.
Bus429 - please check your private messages.
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Through difficulties to the cinema
Just to keep the pot boiling, perhaps the experts here may wish to discuss among themselves what happens if incorrect longitude coordinates are entered into the IRS.
Bus429 - please check your private messages.
**************************
Through difficulties to the cinema
Last edited by Blacksheep; 25th Oct 2003 at 00:34.
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Blacksheep,
A significant positional error entered into the IRU (comared to the last recorded PPOS) will cause the align light to flash, prompting the crew to re-enter the a/c position.
If for some reason the crew were able to enter a wildly erronous position (longitude - I suspect you realise that the entry of a large error in latitude will not allow the IRU(s) to align) then when entering the flight plan, a route continuity (or similar) message will appear as the departure airport will not be the present location.
Even allowing for this, there would be nothing to prevent the crew from selecting ATT on the IRMP, following the system failure, to restore the horizon ball and entering a/c heading to restore the compass rose. It appears from the information we have however that this was not (or could not) be carried out.
P.S. check your pm's
A significant positional error entered into the IRU (comared to the last recorded PPOS) will cause the align light to flash, prompting the crew to re-enter the a/c position.
If for some reason the crew were able to enter a wildly erronous position (longitude - I suspect you realise that the entry of a large error in latitude will not allow the IRU(s) to align) then when entering the flight plan, a route continuity (or similar) message will appear as the departure airport will not be the present location.
Even allowing for this, there would be nothing to prevent the crew from selecting ATT on the IRMP, following the system failure, to restore the horizon ball and entering a/c heading to restore the compass rose. It appears from the information we have however that this was not (or could not) be carried out.
P.S. check your pm's
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Finger trouble?
Enter one minute error in Longitude (roughly 67 n.m) and the three IRUs find they are no longer at the last position in which they were shut down. The align lights flash. Re-enter the same coordinates and the IRUs are informed that they have been moved to a new location in the meantime, so they accept that as the new starting position. Now get airborne and the FMS begins position checks and cannot resolve the differences. The FMS shuts down and blanks the Nav displays - NCD.
Nothing to do now but select ATT, enter heading from the standby compass and cry for help from ATC.
**************************
Through difficulties to the cinema
Nothing to do now but select ATT, enter heading from the standby compass and cry for help from ATC.
**************************
Through difficulties to the cinema
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"Enter one minute error in Longitude (roughly 67 n.m)..."
And speaking of finger trouble...
I think you meant to type in one degree, Blacksheep... otherwise the world would be 1,447,200nm in circumference (unless I've hit the wrong buttons on my calculator ).
I'm wondering how long it would take to confuse the IRS's if you only had one minute of error?
Regards.
Q.
P.S. As co-incidence would have it, carrying out a Nav Database load last night on a 767 and experiencing some problems getting the FMC to accept it after a power interrupt half way through... I experienced a Last Position reset to N0000.0/E00000.0. You can bet I was very careful when entering a new position (after reading this message thread).
http://members.ozemail.com.au/~b744e...000E000000.jpg
And speaking of finger trouble...
I think you meant to type in one degree, Blacksheep... otherwise the world would be 1,447,200nm in circumference (unless I've hit the wrong buttons on my calculator
).I'm wondering how long it would take to confuse the IRS's if you only had one minute of error?
Regards.
Q.
P.S. As co-incidence would have it, carrying out a Nav Database load last night on a 767 and experiencing some problems getting the FMC to accept it after a power interrupt half way through... I experienced a Last Position reset to N0000.0/E00000.0. You can bet I was very careful when entering a new position (after reading this message thread).
http://members.ozemail.com.au/~b744e...000E000000.jpg
Cunning Artificer
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Ooops! Finger Trouble!
So, now you see how easy it is then?
[In the days of the steam driven Carousel N00.00.0 E000.00.0 was known as "The Elephants Graveyard" Legend has it that in the seventies, dozens of 747s could be found circling Zero-Zero until they ran out of fuel or their crews awoke from their slumber and entered the next waypoint in the flight plan...]
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Through difficulties to the cinema
[In the days of the steam driven Carousel N00.00.0 E000.00.0 was known as "The Elephants Graveyard" Legend has it that in the seventies, dozens of 747s could be found circling Zero-Zero until they ran out of fuel or their crews awoke from their slumber and entered the next waypoint in the flight plan...]
**************************
Through difficulties to the cinema
Last edited by Blacksheep; 25th Oct 2003 at 10:17.
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What actually happened !!
This in addition to my post regarding the Emergency Landing of Royal Nepal B-757 in kathmandu. Here is the actual copy of the Aircraft Tech. Log book. BTW The crew are still grounded by the F/O Operations Director till date.
Before the Flight (As logged by the Engineer)
1. C IRU INOP & ADD 11001 Raised & Released on MEL 34-21-1 C of C.
After the Emergency ( As Logged by the Cockpit crews)
“Just after Take Off aircraft HSI route went blank with FD, VOR, NDB, A/T, Yaw Damper, FMC, ADF, Autobrk not functioning. Landed back in Kathmandu with the only reference to Magnetic Compass.”
(MCDP Readings):
A/P DISC.
IRU C/FCC C;
A/P DISC
IRU L
A/P DISC
IRU R
A/P CTN
MODE ERR:
After the maintenance work was done (As Logged by Engineers in the Logbook)
1. L FMC replaced due route data not displayed on EHSI in map mode database updated. Ref TLP 108675 for FMS. FMS ops chkd satis. IRU ops chkd, Align lights flashing on all positioins aft present position reinserted 3 times, now satis, L IRU replaced as a precaution, all IRU operation checked satis. RDMI indication normal. Yaw Damper test Satis. Auto brake bit shows L IRU, RE L IRU replaced & Autobrake satis.
MCDP test shows L & R IRU/FCC test 01, satis. FMC test 10 Satis. test 30 Satis.
2. Over diffected Nav system’s indication & test normal.
3. CTR IRU SWAPPED WITH R IRU Defect remains. Returned to original position co-ordinates re entered 3 times, now OK FLT evaluatioin RA 409/410 date satis. cleared.
Any ideas & comments experts ?
Before the Flight (As logged by the Engineer)
1. C IRU INOP & ADD 11001 Raised & Released on MEL 34-21-1 C of C.
After the Emergency ( As Logged by the Cockpit crews)
“Just after Take Off aircraft HSI route went blank with FD, VOR, NDB, A/T, Yaw Damper, FMC, ADF, Autobrk not functioning. Landed back in Kathmandu with the only reference to Magnetic Compass.”
(MCDP Readings):
A/P DISC.
IRU C/FCC C;
A/P DISC
IRU L
A/P DISC
IRU R
A/P CTN
MODE ERR:
After the maintenance work was done (As Logged by Engineers in the Logbook)
1. L FMC replaced due route data not displayed on EHSI in map mode database updated. Ref TLP 108675 for FMS. FMS ops chkd satis. IRU ops chkd, Align lights flashing on all positioins aft present position reinserted 3 times, now satis, L IRU replaced as a precaution, all IRU operation checked satis. RDMI indication normal. Yaw Damper test Satis. Auto brake bit shows L IRU, RE L IRU replaced & Autobrake satis.
MCDP test shows L & R IRU/FCC test 01, satis. FMC test 10 Satis. test 30 Satis.
2. Over diffected Nav system’s indication & test normal.
3. CTR IRU SWAPPED WITH R IRU Defect remains. Returned to original position co-ordinates re entered 3 times, now OK FLT evaluatioin RA 409/410 date satis. cleared.
Any ideas & comments experts ?
