Honeywell Aerospace Airbus General FAQs

1. What is the value of the Tropopause entry on the Init page of the FMS and should the entry be changed from the default -56/36090 during preflight? The FMS uses air density calculations for it's predictions. The slope on a graph created by plotting a line from the current aircraft sensed temperature and altitude to the Tropopause is key to these predictions. The definitions of the atmosphere's layers follow. The ICAO Standard day is a surface temperature of 15 degrees Centigrade and a 2 degree decrease in temperature per 1000 feet, up to 36090 feet, above which the temperature is a constant minus 56 degrees centigrade. The Tropopause the line separating the Troposphere from the Stratosphere. The Stratosphere therefore by definition is a minus 56 degrees Centigrade until reaching approximately 50 miles where the Ionosphere begins. Therefore, the Tropopause is the transition between the Troposphere and the Stratosphere. There is variation to this standard day and this is known as the "Delta T". In the summer in mid latitudes I have observed a plus 16 degrees Delta T on rare occasions. This means that at 36090 feet the temperature may be as much as 16 degrees warmer and the Tropopause may not occur until an altitude of 44090 feet. Recommendation: If you do not know the altitude of the tropopause for a flight, leave it alone. Leave the default entry. Your predictions may be slightly affected by this. I observe that most airlines have the policy that if this is unknown, then they do not change it. On some Airbus aircraft, the actual tropopause may exceed the entry limit, therefor do not enter 440 for 44090. The system will erroneously use the 420 feet for predictions and this will surely cause erroneous predictions

2. Should the Tropopause entry be changed during flight? There is no precedent for changing the tropopause entry during flight. Recommendation: If one insists on modifying the default number, do it once before flight, and then use an altitude that is a computed average for the flight.

3. The most basic of questions. I am not technically oriented so even the most basic concept of VOR/DME is mysterious to me. OK, you hard tune xyz vor on the captain's side. So, whatever you have tuned will be displayed on the ND until you are out of range to receive it and/or it is behind you. If you never 'release' the frequency on RADNAV you have no VOR bearing info to the FMGC (assuming you are out of range of the hard tuned VOR. The DME freq associated with that navaid is also locked in and you will lose that one dme freq as soon as you are out of range. It is my understanding that you can fly all the way across country and if you never release the hard tuned frequency (xyz) you simply lose display on the ND and of course bearing (VOR) updates. You (the fmgc) still have the capability to auto tune 3 dme's and use them for fixes. It is also my understanding that the FMGC doesn't like to use VOR/DME for fixes anyway. Its first choice is DME/DME so in all probability you lose only display on the ND when you

forget to release a hard tuned vor on the RADNAV page. Is this about how it works? I have read your honeywell manual over and over but it is a little unclear to me. Thanks. Your NAV radio has the ability to tune many frequencies during any one second and also get the needed data in the same one second time frame. If you look at the Selected Navaids Page, you will see that navaids that are being tuned in any one second. The radio tunes each of the fields shown. The LSK 1 line is the navaid tuned for display, the LSK 2 and LSK 3 fields are the navaids tuned for DME/DME position and the LSK 4 is the field showing the tuned ILS frequency. The LSK 1 tuned Field is always the procedure specified navaid for display. That is, this is the navaid that the FAA thinks that you should be tuning and it will automatically change at the charted or otherwise designated changeover point. If you hard tune the frequency on the Rad Nav page etc, then you have precluded only this selection. the other processes will continue to take place for aircraft position determination, i.e., DME/DME or DME/ Azimuth. The DME/DME is known as Rho/Rho and DME/Azimuth is known as Rho/Theta. The most accurate navigation position with Radio Tuning is Rho/Rho next is Rho/Theta. I question the validity of anyone tuning a specified navaid manually unless you know of a specific problem or have a unique need that we should alert the authorities to and then it may be best for me to look into the problem first. I do have one scenario where you might tune the ILS frequency in the VOR slot when you need ILS DME for reference for a departure turn. Then you can see the ILS DME on the ND in the tuned VOR location with it's DME for that unique departure. If you forget to deselect or CLR the selected frequency when it is no longer appropriate via the Rad Nav page then a Fed could question your selection or procedures. The system is designed to insure that the appropriate navaid is tuned for display and identified to you on the ND. in the lower corners. Now if you want the tuning to stop for all navaids on FMS 1, then Lift the guard on your Radio Management Unit (Comm Radio) for the NAV and then tune the radio on it. When the RMU is selected manually, then that on-side FMS is not allowed the use of the radio for navigation tuning of any kind. So, the only way to stop the FMS from acquiring Radio FMS position is to activate the NAV on the RMU. The other side FMS will continue to acquire radio tuned position unless you also select NAV on the RMU for that side also. If you have GPS the navigation source with the smallest Estimated Position Error will be the source used by the FMS for aircraft position. In almost all cases this will be GPS if so equipped.

4. Does the Airbus family of aircraft (except the A310) consider engine anti-ice in the calculations to build the descent path? No! When Anti-Ice is required during the idle segment descent path inthe FBW airbus aircraft, the increased engine rpm and obvious thrust is not accounted for in the computed

aero model. Therefore, the aircraft has difficulty remaining on the vertical path without pilot intervention, i.e., speed brakes.

5. Why does the aircraft slows in certain conditions when a new higher than planned altitude is selected on the FCU? The problem occurs when a climb is initiated above the original entered INIT A page altitude or the current PROG page cruise altitude. A message in the SP "NEW CRZ ALTXXXXXX" is displayed. You must reenter the CI after this to get the best Cost Index speeds during and following the climb and cruise. The Software internally and invisible to the user has defaulted to Zero. Re-entering the displayed CI on the PERF page will result in an acceleration to the previously entered Optimum CI speed. The problem is fixed in Pegasus, but not in Legacy (A340 L9.6) or A320GPS. Description of the problem and fix follows... In Legacy I observed the following: In CRZ at FL250, CI= 30, PERF page is CRZ with managed speed 0.67M (CAS 279kts). Enter FL330 on PROG page with no FCU alt change. PERF page changes to CLB with managed speed 265/. 75 and a/c slows to the lower CAS target. (This new lower CAS 265 kts is not from CI=0, it is the CAS equivalent to 0.75 M at FL330.) Re-entering the CI=30 again causes 284/. 75 to be displayed and a/c accelerates to the higher CAS target, which is the CAS part of a 'normal' CLB CAS/Mach schedule. In Pegasus with the same initial status the entry of FL330 does not cause a change to CLB on the PERF page. Instead the flight phase remains CRZ and 0.75M is displayed. A/C now accelerates to CAS 314 kts, which is 0.75M at FL250. Dialing the FCU alt up causes the a/c to climb at constant 0.75M to the new CRZ FL 330.

6. Is there any way to enter " light & variable" winds into the approach phase? A non-entry on the PERF Approach page defaults to Zero. If the winds are really light and variable, Ground Speed Mini is designed to taker care of this situation and no entry is required. However, if the winds are identified as 250 @ 10 enter these into the PERF Approach page and Ground Speed Mini will also account for these winds.

7. On the hold page, confirm please that the "LAST EXIT" time and fuel is the computed time to leave the hold, proceed to the destination, shoot an approach and missand proceed to the alternate and land with the fuel minimums specified in the FMS Airline policy file. The "LAST EXIT" Hold time is based on the above with the reserves specified by the company in the NDB Airline Policy File (Legacy) or the FMS Airline Modifiable Information file (AMI) in the Pegasus system.

8. Does Localizer updating occur with GPS as the primary means of navigation for all Air Transport aircraft? LOC correction is applied to aircraft position regardless of whether a GPS navigation updating mode is selected, as long as the flight plan specifies an approach type that is one of ILS, LOC, MLS, LDA, IGS, SDF, or BAC.

9. What causes a map shift? Known Causes of Map Shifts

A map shift will occur if: GPS is Not Primary and one or more of the Rho/Rho navaids used at any one time are located at a latitude/longitude that is not consistent with that published by the local authorities and used in your Nav Data Base. This is WGS-84, but in the wrong location. A map shift will occur if: GPS is Not Primary and the Published " Magnetic Declination" of a Rho/Theta station is incorrect. Declination is the orientation of the station to Magnetic North at the time the station is planted in the ground or last surveyed. This is not today’ s Magnetic Variation, it is the variation at that station when installed or last corrected. This will cause map shifts when in Rho/Theta. A map shift may be required even if GPS is Primary and an ILS is selected and when within 20 nm of the runway. The alignment of the localizer or localizer beam of an ILS with reference to the precise extended centerline of the runway and divergence from the published inbound course will cause a lateral only Localizer update map shift. This occurs prior to the aircraft intercepting the localizer beam. A map shift will occur if GPS is Primary, the aircraft is within 20 nm of the airport, the Approach type selected is a specific ILS where the same frequency is used for both ends of the runway. In this case, the two DME transmitters are co-located and the FMS system autotunes for the selected approach ILS DME and the DME for the opposite end of the runway is transmitting. If the specified Figure of Merit priority is 5 or greater in the Nav DB,then that DME use is precluded. When the Map Grid system is not WGS-84, serious map shifts will occur. The ICAO signature countries affirm that they will use WGS-84 by the end of 1998. (It must be noted that Nonon-compliant country has begun to publish the WGS-84 data. Jeppesen, Swiss Air and other NDB suppliers are concerned. There is no motivator to entice the Non-compliant world to change.) Trimble resolved the problem in the Honeywell (HT1900) Navigator by developing a program that converts all the non-compliant grid systems to WGS-84. This leaves non-ICAO countries in-non-compliance and our Navigation systems cannot work reliably. A map shift will occur when a software bug is introduced. This is the case when a pointer in the operating software to create a "Place Bearing Distance" waypoint from a VOR or using Rho/Theta for a navigation track uses current Mag Var instead of Mag Dec from the Nav Data Base. So, a VOR referenced PBD must use the Mag Declination for that station to create the PBD. Other waypoints (not navaids) must use the current location Mag Var. Each degree of error at 60 nm causes a one-mile position error. This problem is corrected in the A320, 330, 340 software. It still remains in some other systems.

10. How do I clear the overfly once it has been inserted? An automatic deletion by button push was considered, but the only way to remove remains to delete the overfly waypoint and then reinsert the waypoint.

11. Why does the OPT altitude on the PROG page sometimes differ from the OPT calculation on the STEP ALTS page? It appears that the PROG page and the STEP ALTS page may use a different calculation to determine the optimum altitude. If this is the case, which one is more accurate? There are two functions being computed. Optimum Altitude is defined as the altitude where the Cost Function is minimized for a cruise flight segment of at least 15 minutes in duration. The Cost Function is based on the total fuel flow, the Cost Index, and the average ground speed over the next 500 NM of cruise. The Cost Function is computed at

various trial altitudes, in 500 foot increments from 25,000 feet to the Recommended Maximum Altitude (REC MAX ALT). The altitude with the minimum cost function becomes the Optimum Altitude.

The Optimum Step Point is a point on the flight plan predicted by the FM for which savings, in terms of fuel and/or time, will occur if a step climb to a specified altitude is initiated at that step point rather than flying the vertical profile of the original flight plan. In this function, which is more of a process, the computer makes simulated flights of the whole flight plan with different step points selected and then selects the step point at which the best savings occur. Summarizing the use of the two functions I would regard the OPT ALT function as a tactical optimum altitude whereas the STEP OPT ALT function is a strategic one.

12. How many stations does the Airbus FMC auto tune at any given time? Up to four each second.

13. How does MDA entry and final approach affect flight path and FMC altitudes and phases of flight? The MDA entry is for Pilot awareness only. Flight path and phase are in no way related to MDA entries.