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Dual FMC failure Boeing 737 ng

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Dual FMC failure Boeing 737 ng

Old 8th Apr 2011, 14:31
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Dual FMC failure Boeing 737 ng

what should be the course of action in case of Dual FMC failure in Boeing 737 ng ?
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Old 8th Apr 2011, 16:03
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Dust off the PLOG and QRP.
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Old 8th Apr 2011, 16:15
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Use IRS for Lat-Long. Plot it on the Jepp say every 10 minutes or so. Since you would still have a Track Line available, you can use the ND to navigate using the following method:
*Set the Track Required in the MCP Course Window.
*Set the ND to CTR VOR mode.
*In the ND you will have the hollow Course needle and the white track line. The course needle is your Track Required[TR]. The Track line is your Track Made Good [TMG]. Use HDG SEL to turn the aircraft to keep the TMG line inside the TR line.
*This way you will be able to give wind corrections, make airway course changes etc with a bit of ease.

Hope this helps
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Old 8th Apr 2011, 19:33
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Or if you are within range of a VOR you could just use VORLOC and ALT HLD and resume conventional NAV
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Old 8th Apr 2011, 21:35
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No FMC, no RNAV capability. Therefore not approved to use european airspace flying IFR except with special permission by every concerned ATC unit. So inform ATC and ask for vectors to the next airport.

Judging from our OFPs (LIDO) it isn't required anymore to have all waypoints or even all airways on it and therefore is not usable for navigation.

Actually had a case of FMCs being unable to "talk" to the rest of the airplane which resulted in autothrust always trying to achieve 104% N1 regardless of actual speed and MCP selected speed. If the same is true with completely failed FMCs you probably have basic autoflight modes, but no autothrust anymore which shouldn't be a problem though for any halfway competent pilot.
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Old 8th Apr 2011, 22:22
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All perfomance related calculations must also be conventionally done, like TOC (if relevant), TOD, actual weights and respective speeds.
Regarding this topic I recently had an FMS unable to give any performance outputs on a 737 classic: not a too big deal, but workload, especially on really short sectors, might slightly increase.

p.s. my first post (tech-log, I am pretty brave!) but a long-time reader. Hello everybody
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Old 9th Apr 2011, 00:52
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what should be the course of action in case of Dual FMC failure in Boeing 737 ng ?
You do the "FMC Fail" non-normal checklist of course:

1 Resume conventional navigation. Without an operating FMC, LNAV and VNAV are not available.
2 When preparing for approach: Use the manual N1 set knobs to set the N1 bugs.
----

I had the pleasure of this a few weeks ago. With a "dual" FMC failure in a classic. Well... actually there is only one FMC in most classics, but the result is the same as a dual fail in an NG = "FMC FAIL" written on both CDUs and loss of map mode on both sides.

ATC was informed and we got vectors for the remaining 1 1/2 hour flight, since our route was mostly RNAV points. The checklist was read and approach speed and go-around N1 was looked up in the QRH. Flight progress was checked by looking in the Jeppesen charts and finding appropriate VORs where our flight plan points could be located with a radial and DME distance, so that we would have an idea when passing abeam them. During descend it started working again with the message "select active waypoint" which is normally assosiated with a power loss - probably condensation somewhere in the wiring I would guess - it was bloody cold that night.

We didn't have endless amounts of fuel so without the FMC prediction for fuel at destination, it was a bit uneasy feeling until we got a system going with VORs for cross checking our position. Otherwise it's no big deal.
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Old 9th Apr 2011, 03:50
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Yeah, don't bother with the peanut gyro, VOR, DME, and ADF. It's over.

Once you can't see your little airplane on the screen moving around, toast.
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Old 9th Apr 2011, 08:16
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Its no biggie other than that you are stuck with conventional navigation and manual performance calculations, as previously mentioned Happened during my last sim ride (both boxes went blank, Map display blanked), interestingly enough without intent from the examiner - turned out that the sim became desynchronized, we continued flying nonetheless, became an interesting lesson after all...
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Old 9th Apr 2011, 08:57
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Standard fit in an NG is the same as the -300: Two Control and Display Units (CDUs) feeding ONE Flight Management Computer (FMC), however dual FMCs are an option, as are Alternate Navigation Control and Display Units (ANCDUs)

ANCDUs are a CDU with the addition of a basic area navigation (i.e. LNAV, but no VNAV) computer installed. You will know if you have this option as you will have and Alternate Navigation Switch (ANS, with positions L and R) on the glareshield to direct the correct nav inputs to the autopilot.

If you don't have ANCDU backup:

Take-Off & Climb
  • Navigation is not normally permitted in B-RNAV (RNP 5) airspace, however is it normally OK to proceed to a repair airport with ATC informed. (Jeppesen Text, ATC pages 551-554)
    .
  • MEL 2-34-27 is applied, some MNPS airspace routes must be avoided.
    .
  • The Repetitive Flight Plan (RPL) must be cancelled, and a new plan filed with "S & R" in item 10 removed. "STS/NONRNAV" must be entered in item 18.
    .
  • The phrase "Negative RNAV" is appended to each radio message on initial contact with each ATC frequency change.
    .
  • Obtain the take-off N1 from the QRH "TAKEOFF N1%" page (it used to be PI 10.11), or the "ASSUMED TEMPERATURE REDUCED THRUST" PAGE (PI 10.12-13)
    .
  • Set the calculated take-off N1 on the PF's N1 bug, using the manual bug procedure.
    .
  • Calculate the MCT thrust (QRH PI 13.2) and set that on the PNF's N1 bug using the manual procedure (in case of engine failure)
    .
  • MCP settings are normal (except no LNAV or VNAV), set the EHSI to VOR/ILS rose or expanded, as appropriate for navigation.
    .
  • AUTOTHROTTLE is not available for take-off - set thrust manually prior to 80 knots.
    .
  • Climb power may be set by selecting the AUTOTHROTTLE selector to ARM, and pressing the N1 button. (at thrust reduction altitude.)
    .
  • Pitch modes available for flight are: TO/GA, LVL CHG and V/S (no VNAV)
    .
  • You will need to navigate by HDG and/or VOR/LOC.
    .
  • Once established on outbound track and above FL150 disengage the AUTOTHROTTLE (or deselct N1) and periodically set the N1 climb limit on both N1 guages as per QRH MAXIMUM CLIMB % N1 (PI 10.14) every 4-5000 feet.
    .
    (As the Power Management Computers (PMCs) are using inlet temperature and pressure data (Pı,Tı sensed from the probe in front of the engine's fan) they have a very conservative schedule, so a significant performance degredation occurs as the aircraft climbs. There is no climb performance table information from the FMC, so the AUTOTHROTTLE will attempt to maintain the lower thrust if used in the climb)

Cruise
  • Approaching cruise level, extract the target N1 from (QRH PI 10.15 FLIGHT WITH UNRELIABLE AIRSPEED/TURBULENT AIR PENETRATION (Cruise), and set this number on the PNFs N1 guage.
    .
  • Reaching cruise level, extract Limit N1 from the QRH MAXIMUM % CLIMB page, and set on the PF's N1 guage.
    .
  • Autothrottle can be used to maintain cruise speed. Company rules vary, but generally without ECON cruise, LRC cruise is used (it could of course be a fixed MN cruise).
    .
  • Navigate Raw data (or radar vectors if you have no shame about not being competent enough to fly an aircraft ), and don't forget to inform ATC you are not RNP compliant.

Descent - Approach
  • Calculate your descent point from the chart M0.74/250 KTS DESCENT SPEED (ALL ENGINES) (PI 11.5)
    .
  • Prior to commencing descent, bug the Vref speeds, using the VREF chart (QRH 10.3)
    .
  • Once the ATIS is received, set the N1 guage cursors to cover a missed approach or Go-Around from the QRH GO-AROUND % N1 chart (page PI 10.14)
    .
  • Descend at your company speeds - M0.74/280/250, for example.
    .
  • Use Raw data below MSA, ensure the EHSI mode selector is at VOR/ILS
    .
  • Auto-throttle may be used throughout the descent and approach.
    .
  • In the event of a missed approach, pressing the TO/GA buttons will cause the AUTOTHROTTLE to disengage, and the thrust levers will have to be manually advanced to the previously buggeed N1 limit. The flight director will correctly display TO/GA commands.

N.B. : experience shows that FMC failures are usually of relatively short duration, if operating in ANCDU with IRS pages displayed on the CDU there will be no indication of FMC reset. Press any of the top two rows of keys on the CDU (INIT/REF, RTE, CLB etc) to test FMC status

Last edited by Checkboard; 9th Apr 2011 at 09:24.
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Old 9th Apr 2011, 19:26
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Navigate Raw data (or radar vectors if you have no shame about not being competent enough to fly an aircraft )
I do see the smiley, however maybe a bit too smart alec comment anyway.
Please do tell me how to fly direct to RNAV point "NOVOR" raw data?

Of course you can request direct to Im-da-man VOR, but if the airspace is complex enough, you find that ATC will prefer to keep you approximately on the filed RNAV route with vectors that you don't interfere with other airways. Have a look at your enroute charts for eastern-europe and you will find that most airways practically contains zero VORs or ADFs.

Calculate your descent point from the chart M0.74/250 KTS DESCENT SPEED (ALL ENGINES) (PI 11.5)
Or nm = height x 3, if you like to keep it simple
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Old 9th Apr 2011, 20:35
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Please do tell me how to fly direct to RNAV point "NOVOR" raw data?
When you were flying little aeroplanes, how did you find a town, or turning point without a navaid at the point you are looking for?

It's called navigation - you have a working clock, a working heading reference, you can plot a fix to determine your current position ... In your particular case - the dual IRS's in the 737 were still working, all you had to do was look up for your actual track & ground speed, and get a chart out to see where the place was.

"Children of the Magenta line" indeed - that pilots today even have to ask how to do it, as though it is an impossibility without vectors, shows quite a bit.


In Australia, after the Omega navigation system was decommissioned, my airline had us flying with no area navigation system at all in a BAe 146 - just NDBs and VORs. On many of our routes we were completely outside navaid coverage (of any sort) for up to an hour. In one instance I was flying an aircraft with an unserviceable autopilot from Cairns to Darwin and had to divert north around a cyclone in the Gulf of Carpentaria.


The solution (diverting left and right around thunder heads, outside navaid coverage of any sort, without autopilot) was simply to get a chart out, and run a series of air plots for each change of heading for an hour, then apply forecast wind vectors to ded-recon to a point back on the airway, and pick up the VOR radial.

Last edited by Checkboard; 9th Apr 2011 at 21:53.
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Old 9th Apr 2011, 20:39
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Or nm = height x 3, if you like to keep it simple
+1nm for each 10knots IAS deceleration, still to keep it simple
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Old 10th Apr 2011, 00:03
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It's called navigation - you have a working clock, a working heading reference, you can plot a fix to determine your current position ... In your particular case - the dual IRS's in the 737 were still working, all you had to do was look up for your actual track & ground speed, and get a chart out to see where the place was.
I asked you how to proceed to an RNAV point raw data, not by proceeding VFR or Dead reckoning.

Neither hardly wise choices in congested RVSM/RNAV airspace.

For data to be "raw", there needs to be data in the first place. That means that you have the ability to track some form of navaid which provide data.

Did you even consider the drift of the IRSs???
Such old ladies are not the most precise, and I may remind you that the updating from VOR/DME is applied to the FMC (which just failed). Hence you are left with a position that may have several hours of flight time and thereby drift - perhaps 10 miles or more. So what is the accuracy of your navigation when you include the accuracy of your DR?

Sometimes it's good to be cleaver, and sometimes it's better to leave out the completely irrelevant anecdotes (plus insults).

Last edited by cosmo kramer; 10th Apr 2011 at 00:30.
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Old 10th Apr 2011, 03:25
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Cosmo,
I asked you how to proceed to an RNAV point raw data, not by proceeding VFR or Dead reckoning.
Providing you have a VOR/DME in range, you can use the fix-to-fix navigation technique. It takes a quite a bit of practice and mental gymnastics but for two crew should be doable. I'll conceed that it maybe a bit but unrealistic in modern airspace given that when vectors are unavailable, so are navaids!

As for IRS drift, the 737 Clasic is meant to be RNP 12 without updating. In my experience I wouldn't bank on it though!

And another exclamation mark for good measure!
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Old 10th Apr 2011, 08:34
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I asked you how to proceed to an RNAV point raw data, not by proceeding VFR or Dead reckoning.
... and it still startles me that you think this is difficult !! I was pointing out that the IRS is available by switching the IRS panel to track mode, which will give you a very accurate track - i.e. no wind calculations!

So, to spell it out:
  1. FMC fails.
  2. Select HDG on the Mode Control Panel.
  3. Complete QRH checklist(s).
  4. Inform ATC NON-RNAV.
  5. Get chart out of folder and determine current position, from last recorded fuel check on the PLOG initially then by local VOR.
  6. Obtain airway track from chart and maintain that using HDG bug, aided by current track from IRS panel on the overhead (IRS position drift is irrelevant).
  7. Approaching RNAV position, dial up suitable fix combination - VOR/VOR or VOR/DME.
  8. As the aircraft approaches the fix, it will intercept one of the fix criteria before the other (assuming you are slightly off track) - ie one VOR radial before the other, or the DME arc before the radial. Slightly adjust the HDG bug to track the aircraft along the first intercept until you are at the second (fly the aircraft into the 'V' of the fix)*,
  9. at the fix, turn HDG to next track - correct tracking using the TRACK display on the IRS panel overhead.
  10. Write down time at fix. Note Groundspeed from overhead IRS panel. Calculate time to next fix (or just use the PLOG planned times - but personally I would work out my own).

The saying is that pilot's earn their larger-than-bus-driver wage not when things are going fine, but when things go wrong. Personally I would be professionally ashamed to ask for ATC help to navigate my aircraft, when no Navigation equipment on the aircraft had failed - just the box that did the navigation thinking.

*,(I was going to mention the fix-to-fix thing (although I never called it that) but thought it too complicated. Good link, though.) I would use that approaching the RNAV fix point.
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Old 10th Apr 2011, 09:31
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The saying is that pilot's earn their larger-than-bus-driver wage not when things are going fine, but when things go wrong. Personally I would be professionally ashamed to ask for ATC help to navigate my aircraft, when no Navigation equipment on the aircraft had failed - just the box that did the navigation thinking.
And at the subsequent board of enquiry when the aircraft is laying in flames and the court says "Mr Pilot, why is the aircraft laying in flames?" and you can reply " I was ashamed to ask ATC for help when my navigational box failed, I know there is an X million pound radar system down there and I know I was wrong in my calculations but at least I tried"

Personally I'd get as much help as possible!!
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Old 10th Apr 2011, 09:42
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Perhaps given the standard of respondents here, and their level of confidence in their professional piloting abilities, failing to find and maintain a heading, given two IRS's to help, IS too dangerous for them.

To think that Area navigation has only been around in my lifetime ... Mick O'Leary is right - pilots today are only bus drivers, worth £20,000 a year.
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Old 10th Apr 2011, 11:09
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You are not answering my question. You are just repeating yourself, with the same dead reckoning bs (and condescending tone). You are advocating to take an unprecise starting point, apply an even more unprecise methode, to find a point that ATC expects you to overfly with great accuracy. Great airmanship!
Personally I would be professionally ashamed to ask for ATC help to navigate my aircraft
Pride is a really nice quality to bring to an aircraft too.

It's not about being dangerous or difficult, it's about being inappropriate. I would happily fly DR if the FMC fails when no navaids or radar coverage is available - hardly the case over eastern europe.

Sciolistes, thanks for the link. Yes probably not very useful when you go 8nm pr. min, and again like DR too much of inaccuracy. And when starting to turn 30 deg off track to find an initial heading ATC it probably going to ask "confirm inbound XYZ".

Last edited by cosmo kramer; 10th Apr 2011 at 11:52.
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Old 10th Apr 2011, 12:13
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You are advocating to take an unprecise starting point
In what way is a local VOR fix "unprecise"?
apply an even more unprecise methode
In what way is tracking information from a Dual IRS not precise?
to find a point that ATC expects you to overfly with great accuracy.
What part of "The phrase "Negative RNAV" is appended to each radio message on initial contact with each ATC frequency change." do you or ATC not understand?
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