Airline FMS Support Frequently Asked Questions

Honeywell’s flight management systems (FMS) are supported by expert technicians to protect your investment, maximize efficiency, and ensure safety. We provide important guidance, resources, and documentation to enable you to address issues as they arise. The answers below address frequently asked questions that share information on support details ranging from how to find publications to topics based on loading a Navigation Database.

Q: Where do I find Air Transport Engineering publications? 319, 320, 330, 340, 737, 727, 747, 757, 767, 777, MD-10, MD-11, MD-80, MD-90, 717, DC-10? A: A listing of all documents are here: Copy and paste the document number in PDL and select 'search all' to bring up the document. 

Q: What is the life of a Mass Memory Card Lithium Battery? Is there a spec for it? A: The manufacturer's spec for the life of a Lithium Battery we use in the MMC card is between 8 and 10 years. However, to be absolutely safe, we recommend to replace both the battery in the MMC card every four years. This is mentioned in the CMM as well. The Spec is provided in the attachment.

Q: Will IRU cause FMS to drift in flight? A: This problem may be cause by IRU position not set correct at initialization. FMS will be updated by GPS and short range sensors, when over water GPS down, FMS drifts off to IRU. It will correct itself once GPS or short range sensors are available. 

Q: Can data be fed directly into the FMC - from the ACARS -- such as uploaded data including winds, three/two engine flight plans, as well as diversion flight plans? A: If you have ACARS you can certainly uplink flight plan and wind data. As in any Boeing FMC there are only two flight plans to work with Active and Provisional. You will have the route you are flying in one and then one provisional route to play with.

Q: Can the Pilot manually stored Waypoints be lost when FMC power cycles? Will loading the new NavDB erase the manually stored waypoints? What condition could cause the manually stored waypoints to be lost? A: Stored waypoints are deleted or retained when the FMS transitions to DONE phase. Done Phase is typically 30 secs after Engine Shutdown. Pilot Defined Elements will not be lost during a FMC power cycle. But they will be lost when a new NavDB is loaded.

Q: Why are some of my FM features disappearing when I load a NavDB provided by another airline where my aircraft was C-checked? A: The airline policy file defines all the FMS features to be enabled with the NavDB. If these features are not enabled by airline policy data in the NavDB, even if the airplane has all the equipment to support these features, the features will not be activated.

Q: Why would a FMC fail after loading the latest cycle of the NDB and checking the correct part number on both MCDUs? A: The B747-400 FMS does not crossload. Seeing the same NDB part number on both left and right MCDU IDENT pages can be misleading. This can happen when the NAVposition on both the Captain and First Officer Source Select Switches are selected to the same FMC. That being the case, both MCDUs are showing the same NDB part number from either the left or the right FMC but not from both. And when the NDBs are not the same between the two FMCs, there will be no failure or miscompare indication while the airplane is on ground. This can explain why LM is not aware of the discrepancy. However, after the next take-off, the second powered up FMC will latch fail. The FMC Bite data will log a "Indep Mode & Airborne" fault. To prevent this mistake, both FMCs have to be individually updated with the NDB, the NAV switch selected to its on-side FMC (or the pointer on all the switches on the Source Select module set to the vertical position), and then then NDB part numbers verified for correctness.

Q: To assist in troubleshooting and investigation, BITE should be downloaded from the FMC. How long will the relevant data be stored before being written over? A: BITE dump from the FMC if retrieved too late will not have the concerned flight data to help in any investigation. The FM bite should be downloaded as soon as possible for a crew reported event before they get overwritten and 5 days should be a limit.

Q: When does radio updating of FMC position begin after takeoff? A: Position is updated as soon as the FMC tuned radio has valid data, on the ground or in the air.

Q: What’s the value and units of Cost Index entered from MCDU? A: The cost index varies from 0 to 9999 and is determined by dividing aircraft operating cost ($/hour) by fuel cost (cents/pound) in case you have Imperial units and is determined by dividing aircraft operating cost ($/minute) by fuel cost ($/kilogram) in case Metric units.

Q: Reference PRNAV operational approval: how can flight crews confirm that an Approach Procedure has been coded correctly with respect to Overflys? A: Airbus and Boeing FMCs operate differently. On Boeing FMCs, there is no Overfly indication given on the MCDU Flight Plan pages, while on Airbus FMC, Overfly indication is given. Flight crews, therefore, need to review the Overfly transition on the Nav Display on Boeing aircraft to confirm that it is drawn correctly.

Issue: FMS does not autotune the ILS for a specific approach Resolution: The FMC will not auto-tune the ILS if the approach procedure is coded with TF (Track to a Fix) leg, since a TF leg by definition does not have an associated Navaid. To correct the problem, the procedure should be coded with CF (Course to a Fix) leg(s). The above applies to Honeywell FMS for Airbus and Boeing models.

Q: Why on an A330 / A340 Pegasus FMS, can Non Directional Beacon (NDB) approaches not be selected even though they are incloded (coded) in the loaded Navigation Database (NDB)? A: To select any of the NDB approaches included in the Nav DB, the operator needs to have the Airbus OPC option of "NO ADF ON BOARD" set to NO.

Q: Can the Thrust Reduction and Acceleration Altitude defaults be modified? A: The A300/310 FMC operational software has hard coded defaults of 1500ft AGL for Thrust Reduction Altitude and 3000ft AGL for Acceleration Altitude. But unlike other later generation FMCs there is no database that controls these defaults. These defaults can be manually changed by the Flight Crew but only down to a minimum of 1500ft AGL for both the Thrust Reduction and Acceleration Altitudes. There is a program pin into the FMC that sets the default Acceleration Altitude equal to the default Thrust Reduction Altitude.

Q: After a modification of the Cost Index by the pilot on MCDU in flight, can ground receive this change? When does aircraft send CI to ground? A: CI (Cost Index) is included on FMGC Data Link Performance Data Report (PER). CI on the report is the same value displayed on the CLB, CRZ and DES PERF MCDU page. Pilot can change CI on these MCDU pages. PER can only be sent automatically in response to a ground station request for PER (flight crew initiation of this report is not possible).

Q: Do I need to reload software if swapping Flight Management Guidance Envelope Computers (FMGEC's) between positions 1 and 2 on the same airplane? A: No it is not necessary to reload software when swapping between positions 1 and 2.
Q: Can a NDB used on a FMS 4052506-941 NON PIP be used on a FMS 4052506-941 PIP? A: 1 MEG PIP NDB will work on 1 MEG non PIP and on Pegasus. A 1 MEG non PIP NDB will work on 1 MEG PIP if an APF is added (as part of the NDB). APF (Airline Policy File) is a file that is loaded as part of the NDB and contains parameter settings (airframe/engine) that are similar to the AMI file on Pegasus. APF is provided by the aircraft OEM.

Q: What is the logic in Airbus Step 1A used to produce the AMBER EFOB figure at the destination on the FUEL PRED page (top right), and the EFOB figure on the FLIGHT PLAN page (bottom right), with the resulting AMBER scratchpad message ‘DEST EFOB BELOW MIN’? A: When the predicted EFOB at the destination becomes smaller than the MIN DEST FOB entry, then the EFOB is displayed in amber on the MCDU. As with most indications like this there is a hysteresis of 200kg to revert back to green. So it is possible to have a MIN DEST FOB that is lower than the EFOB but is still displayed in amber. As there is no EFOB comparison between Airbus FM's. The comparison is done on actual Gross Weight – if this differs between FM's by more than 2 Metric Tons then an MCDU scratchpad message is produced.

Q: For the A320 Pegasus FMS, when a pilot changes the Performance Factor will it clear at end of flight? A: Cost Index will remain through both flight complete and a power down. If the Cost Index has not been entered before entering the Zero Fuel Weight (ZFW) on INIT-B Page on MCDU or Gross Weight 9GW) on the FUEL PRED (Fuel Prediction) page, it defaults to the previously entered value (previous flight). Message "USING COST INDEX XXX" is displayed on MCDU scratchpad when the Pilot enters ZFW (Zero Fuel Weight) or GW (Gross Weight).

Q: What is causing excessive residual ground speed reported on all 3 IRUs on CDU "IRS MONITOR" Page on Airbus A310/A300-600 FMS? A: If the aircraft is taxiing on one engine after landing, the problem may be caused by a bad Fuel Flow sensor on the running engine side. The logic for the Residual Ground Speed snapshot is: - Not airborne + Fuel Flow less than 220kg/hr for at least 10 sec on both engines or - Not Airborne + Fuel Flow NCD (No Computed data).

Q: What is the Nav Database (NavDB) capacity of the B757/B767 FMS? A: The memory capacity for the NavDB depends on the version of FMS installed: 1. P/N 4052500-9XX has a NavDB capacity of 200KW (400KBytes) 2. P/N 4052506-941 (PIP) has a NavDB capacity of 1MW (2MBytes) 3. P/N 4052506-955 (Pegasus) has a NavDB capacity of 2MW (4MBytes).

Q: What is the difference in memory size for a Pegasus vs. a 1M PIP FMS? A: 1 MEG PIP is 1 MEG Words which is equal to 2 MEG Bytes. Same with Pegasus which is 2 MEG Words or 4 Meg Bytes. However, for Peg09, the memory size has been increased to 3.75 MEG Words whic is equal to 7.5 Meg Bytes.

Q: Does MD-11 Pegasus FMC's use deflected aileron in its performance calculations? A: The FMS does sense if the aircraft has Deflection Ailerons. If the aircraft has Deflection Ailerons and it is properly wired, the message MD11 DEF AIL will be displayed either on the IDENT or AC STATUS pages.

Q: What FMS standard is required to support FANS on the B757/767? A: Pegasus FMS is required to support FANS. Refer to applicable SBs for upgrade from Legacy FMS.

Q: When automatic Waypoint Reporting is activated crossing the Atlantic, which waypoint triggers the system?  That is, when does the system stop sending position reports? A: WPR (Automatic Waypoint Reporting) has to do with ADS Waypoint Event Contracts. All waypoint sequences trigger the ADS Downlink Report. It is not limited to "Oceanic" or "5510N" (424) formats. The reporting only stops if the ADS contract is terminated by the ground with a "Cancel" uplink.

Q: Is there a bias that says that the GPS signal is X% and the DME-DME is Y%? Is the FMS taking GPS position information also on ground with ground speed less than 100 Kts? A: The GNS position data and the DME position data are NOT mixed. GNS position data is used when the GNS HIL (Horizontal Integrity Limit) is less than the estimated error in the DME position data. GNS position data is also used when on the ground.

Q: Can B747-400 FMS provide data on distance traveled per flight leg. Can you please advise if this is available in the FMC and the procedure to retrieve this info? A: For B747-400 FMS no data is available on the CDU page for the distance traveled per flight leg. It was not a requirement when the FMC was designed.

Q: What could cause a route dump within the FMS when the crews make runway and or SID changes? A: If the crew makes a runway change and the new runway is not compatible with the previously selected SID, the Pegasus FMC software is designed to remove the SID when the runway is changed. The same thing could happen if the SID is changed and it is not compatible with the previously selected runway, the runway will be removed.

Q: I have just updated the FMS OPS software in my B747-400 FMS and the Flight Test Output bus parameters are now missing. What's going on? A: Pins G13 and H13 are the Flight Test Output Bus from the FMC. In the Operators FMS Nav Data Base is a list that maps internal FMS parameters to A429 output labels. When a new FMS OPS release comes out, this list needs updating.

Q: Can FMC P/N 4052506-941 and Pegasus FMC P/N 4052506-955 share the same nav data base? A: Yes, as long as it does not exceed 1Meg.

Q: When the B717 FMS flight plan freezes and cannot be changed, and the rest of the FMS works well, what is the easiest way of unlocking the flight plan? A: Change the Nav data base to the one that is not effective. That will clear the flight buffers. Then, change the Nav data base back to the one that is effective for that time period.

Q: Is there any way, other than cycling power to the FMC, to clear the AOC uplink buffer? A: Yes, customers may use the FMC COMM page to determine if there are any pending uplinks in the buffers. If there are pending uplinks on the buffers, then the associate uplink CDU pages should be used to LOAD or to PURGE the uplinks. Loading and purging the uplinks will clear the uplinks from the uplink buffers.

Q: How long is BITE available in the FMC? A: The 747-400 FMC BITE has only 10 flight legs. On international routes, it takes about 5 to 6 days. However, there is a lot more data in BITE than just in the flight legs. If the incident was caused by a software reset or an auto-throttle disconnect, the data stays in BITE for months. A good rule of thumb is if an FMC related incident occurs, get BITE as soon as possible. If the incident happened a while ago, get BITE anyway since data relevant to the incident may be available. 757/767 Pegasus has 64 flight legs so the data is available for 2 weeks or more. However, if a reset is involved, the data is available usually for more than a year.

Q: After how many takeoffs and landings, the BITE gets overwritten in an MD11 Pegasus FMC? A: The MD11 fault records are organized in 64 flight leg groupings. During normal operation BITE erases the next two legs in preparation for a flight. In addition, the BITE will chain two flight records together if there are a lot of faults recorded. So the best answer is: On a clean aircraft with few faults: approaching 62 flights. On a frequent failure aircraft: greater than 31 flights. Note however, depending on how clean the power ups are on the plane some flight legs can be wasted with false airborne occurrences. This happens when the FMC powers up before some of the other systems and must default to airborne due to lack of input data.

Q: How can a pilot find out if ILS, WPT or airway (STAR) is included on NAV DB uploaded in FMC P/N 4052506-941 on Boeing 767-300ER? A: The best way to determine the information is to use the OneNav tool. The crew can browse for individual “items” such as navaids but not procedures.

Q: What is the limit in term of number of wind uplink for Boeing FMS? A: The character limits for B777 wind uplink is 3360 chars with respect to the actual wind data payload, and excludes any transmission packet headers, end system header data or CRC.  The practical maximum capacity (for a single altitude) is anywhere between 50 and about 110 depending on lengths of waypoint IDs and inclusion of temperatures. The airline can also split a single wind altitude into multiple uplinks if they need to. For B777, “101” reject is received if the Uplink character limit is exceeded.

Q: How can we set metric units for FMS Cost Index? A: OPC software should be changed. Please set FMF METRIC ENABLE to 1.

Issue: A loss of GPS goes to Dead Reckoning outside of Navaid coverage (and with loss of GPS) due to the a/c having VG/DG installed rather than IRS. Resolution: GPS is enabled by an Analog discrete input AND a GPS enable discrete in the Policy File which is part of the NDB Since there is no DAC policy file coded in the data base, which contains the GPS enable switch, it may be the cause of this issue. If it is the absence of the policy file, then the airline must contact Boeing.

Q: If the GPS switch is in the ON state ( "ON" displayed on MCDU POS REF page ) but GPS data is not available, will the runway threshold position (TO/GA) update not be performed? A: Yes, the airplane symbol is updated relative to the runway threshold if the GPS switch is ON (POS REF 3 page, enables GPS updating), but GPS data is not available, just as if the GPS switch was OFF. The reason for this is the system automation irrespective of the switch position. With the loss of GPS data the NAV updating solution reverts to Inertial automatically, therefore allowing a runway position update.

Q: An MD11 operator complained about occasional Excessive Bank Angle Callouts they were getting during take-off on their simulator. Why are they getting those call outs, and how do you prevent their occurrence? A: Bank angle alerts are based on aircraft roll angle versus altitude (AGL). Bank angle limits on the MD-11 varies linearly from 10 degrees at 30 feet AGL to 40 degrees at 150 feet. Above 150 feet the bank angle is limited to 40 degrees. Excessive bank angle Callout will not occur if those limits are not exceeded. This provides protection for over banking maneuvering during climb-out or on approach. It also protects against wing and engine strikes.

Q: Why does my Pegasus FMC MCDU display NAV DATA OUT OF DATE message? After loading a new cycle database into the Pegasus FMC and keep getting the NAV DATA OUT OF DATE message. A: The Pegasus FMC in the Boeing 757/767 aircraft is often configured/wired to receive Time and Date from the Captain's Chronometer and not from the GNSSU/GPS/MMR. If for any reason during aircraft maintenance the Ship's Battery is removed, or disconnected, the database in the Chronometers is lost and its Time  and Date must be reset using the Boeing AMM, otherwise this FMC message will be displayed.   Boeing AMM 31-25-00 Boeing FIM 34-61-00.

Q: What causes a MCDU scratch pad message "CHECK NAV DATA BASE CYCLE" to be displayed consistently -- even when the correct Nav Data Base cycle is selected, and the date displayed on the DOC DATA page (no matter what the source -- GPS or clock) falls within the ACTIVE cycle of the nav db as displayed on the A/C STATUS page? A: This FMS problem was seen on both Pegasus FMCs PN 4059050-921 installed on an MD-11. The source of the problem was that the wrong OPC was loaded on both FMCs on the aircraft. It is very important to verify that the OPC part number is correct for that aircraft tail number. As soon as the correct OPC was loaded in both FMCs the problem was resolved.

Q: What is the valid range for Drag Factor and Fuel Flow Factor for the 757/767 Pegasus FMC? A: For the Pegasus FMC, entry of FF and DF on the IDENT page is in the format of "X.X" with a valid range of -9.0 to +9.9.

Q: An operator experienced a dual FMC failure on a B777-300. What can be the cause, and how can the system be restored? A: Entry of the "SP" key or the "/" key instead of the "DELETE" key when entering the waypoint on the FDCF Position Report page results in a dual FMC failure. A reset of CPM/ACMF (M002) in left and right AIMS will clear the fault.

Q: How to check the Battery Life in B757/B767 FMC? A: Customer should not remove the FMC just to check the battery life. If they do so, FMC has to undergo the whole bench test procedure before getting installed on the aircraft. Customer may want to consider using the low battery power discrete bit transmitted on general purpose bus #1 label 272 bit 13.  If the bit is one, a battery is low.  If the bit is zero, the batteries are OK.  General purpose bus #1 is on A connector pins G09 and H09.  One airline records the bit in DFDR/FDR/QAR data and the bit is periodically examined when the airline obtains the DFDR/FDR/QAR data to process engine parameters that are monitored. If the SRAM battery voltage low condition is true, it is also logged in BITE history following every long term power up.  Battery voltage low is typically recorded in BITE for 2-3 months before the battery voltage goes low enough to cause the unit to latch fail.   Customer could also dump BITE history from FMCs suspected of SRAM batteries near end of life to see if the low SRAM battery fault is being logged.  Checking every 3 months when the unit is suspected of being near end of SRAM battery life would probably be adequate.