Minimum runway length

[Cbf]

Hi Hardy,
For the aircraft model I fly with, I have recently selected 7000Ft/Passenger and 9000Ft/Freighter minimum runway length in the instructor/Model/Programming page. In saved situ former minimum runway length is loaded. To have the new value, I must reload the aircraft model. I think that it is the only solution...
My problem is for alternate airports selected on ALTN page of NG FMC. Even with 7000 or 9000Ft selected in aircraft model, alternate airports with 6000Ft are available (KIPT 6825Ft for example). Is there a procedure to set a minimum runway length for alternate airports in NG FMC?
Thank you

[Hardy Heinlin]

Hi Cbf,

I can't see any problems here. I can save and reload my "Min rwy length" value from situ files. The variable is in the situ file and is called:

CfgNdRwyLim

Re ALTN: It makes no sense to inhibit undesired alternates on the ND only. You should inhibit it on the ALTN page in 5R.

Actually, every airport in PSX has a runway long enough* for a 744 to land on (unless a very unusual type of airport slipped through the database filter). I can proof it; my first landing in a Lufthansa 744 sim was on a 1400 meter runway :-) -- and that's the "historical" reason the PSX databases are filtered by a 1400 meter minimum.


Regards,

|-|ardy


* Referring to the length only, not to the physical structure or width.

[Cbf]

Hi Hardy,
Thank you for your comments.
The problem with short runways may be the width. 45m is convenient for a B744. 30m is still OK. I tried KSEG (22.5m X 1541m). It seems you are landing on a postage stamp...
I checked on FPPM. With a LW of 225T, Autobrake 4, flaps 30°, Sea level, ISA, no wind, VREF+5, landing distance is approx 2000m.

[Britjet]

Don't forget that there is a generous factorisation involved in these figures of 15%, and it also assumes touchdown 460 beyond threshold.
You should be able to stop well within the quoted figures if you plonk it straight on the numbers. Not that you would in real-life, of course..
At light weight - try 1200m :-)
Peter

[DougSnow]

All of our aircraft at work have a minimum runway width of 45m/148 ft.  For our aircraft types (widebodies and the 57), none of the models we fly have a Narrow Runway Appendix to the AFM.  737s and the 320 family, A220, and most of the regionals can go to a 30m wide width, but specific performance issues may need to be addressed. On narrow width runways, Boeing adjusts Vmc scheduling for the 30m wide runways, and there are additional MELs which also come into play.

[Britjet]

Yes, Doug.
Take-off on 30m is also more critical than landing, somewhat surprisingly.
I believe a 30m runway, besides all other approvals, requires a TO2 derate in case of engine failure, so that you don't swing off the runway..

[Cbf]

VMC is a excellent consideration for minimum runway width.
Concerning minimum runway length, the computed landing distance on condition (LW, Alt, Temp, Wind, Rwy slope, Autobrake, Vref+) must be, according to regulations, multiplied by 1.67 to obtain the minimum runway length for destination or alternate.
I would like to know how airline dispatch proceed to determine convenient destination/alternate airports? MLW? A/B MAX? ISA?...
I have an example, LH744 flying to JFK. I suppose approx EW 180T + Load 40T + Fuel 10T = LW 230T. Landing distance (ISA and no wind, A/B 3, Vref+5) = 1700M. Minimum runway length = 1700M X 1.67 = 2839M.
LH B747-400 (even LH B747-800 and EK A380) often land on runway 04R/22L 2560M long.
A difference of nearly -300M. With 30Kt forward wind, it might be OK.

[simonijs]

Hi,

The "1,67" (or 100/60) factor is a dispatch requirement and stems from Annex IV, repeated in EASA/FAA regulations.

In EASA document "Acceptable Means of Compliance (AMC) and Guidance Material (GM) to Annex IV - Part-CAT", in GM1 CAT.POL.A.230 *, you will find:

CAT.POL.A.230 establishes two considerations in determining the maximum permissible landing mass at the destination and alternate aerodromes:
(a) Firstly, the aeroplane mass will be such that on arrival the aeroplane can be landed within 60 % or 70 % (as applicable **) of the landing distance available (LDA) on the most favourable (normally the longest) runway in still air. Regardless of the wind conditions, the maximum landing mass for an aerodrome/aeroplane configuration at a particular aerodrome cannot be exceeded.
(b) Secondly, consideration should be given to anticipated conditions and circumstances. The expected wind, or ATC and noise abatement procedures, may indicate the use of a different runway. These factors may result in a lower landing mass than that permitted under (a), in which case dispatch should be based on this lesser mass.
(c) The expected wind referred to in (b) is the wind expected to exist at the time of arrival.

This then is different from "In Flight" landing distance calculations where latest ATIS weather and actual conditions can be used. Although I am getting 2200 meters of Landing Distance at A/B3, that would fit landing on 22L at KJFK.

Regards,
Simon

*   CAT.POL = Civil Air Transport  Performance and Operating Limitations
**  70 % for Propeller aircraft

[Hardy Heinlin]

Hi all,

airline specific, preferred alternate airports and all the ICAO/FAA specifications and modifications are not implemented in Honeywell's NG FMC. The NG FMC just picks the database airports and sorts the best four airports by the predicted nearest ETA (and by the longest runway, if I recall correctly). That's why the NG FMC offers the possibility to the airline to uplink a list (or two) of alternate airports to the FMC; the FMC will then use that list instead of the database. This feature is also implemented in the PSX network and can be used by flight planning add-ons.


Regards,

|-|ardy

[Cbf]

Hardy,
Thank you for your comments. In case of diversion, I first check the ND to choose an alternate (8000Ft min rwy length selected). I then insert alternate manually on ALTN 1/2 page.
Regards

[simonijs]

The NG FMC just picks the database airports and sorts the best four airports by the predicted nearest ETA (and by the longest runway, if I recall correctly). That's why the NG FMC offers the possibility to the airline to uplink a list (or two) of alternate airports to the FMC; the FMC will then use that list instead of the database. This feature is also implemented in the PSX network and can be used by flight planning add-ons.

Hi Hardy,

Would it be possible to add more filters to the selection of Alternate Airports? I am thinking of IFR capabilities and elevation below the AFM maximum Field Elevation (< 9500 ft).
On ALTN LIST 2/2, for instance, several airports are VFR only for which no charts are available or that are not suitable for the 747 because of elevation.

For a flight Nairobi (HKJK) to Amsterdam (EHAM) the list contains HKRE, HUGU, HSOB (No charts found), HSSM, LGAG (airport not recognized). Or...: should I scan the list (on page 1/2) before/during flight for availability and subsequently use the ALTN/INHIBIT in 5R at regular intervals?

For a flight Buenos Aires (SAEZ) to Quito (SEQM) that list contains SADM, SADJ, SAFS, SPJI (No charts found), SLUY, SLOR, SLCN, SPJL, SPRF, SPZO, SPJJ (elevation well above 10.000 ft, and no charts found for SLCN, SPRF, SPJJ).

No charts found or airport not recognized in the mentioned cases means: using Navigraph, or Aerosoft LIDO charts.

Thank you and with kind regards,
Simon

[Hardy Heinlin]

Hi Simon,

in case an immediate landing is required and an airport above 10000 ft is the only choice, wouldn't you want to consider landing there and wouldn't you want to see that airport on the ND?

Also, the four ALTN airports are just suggestions so that you can evaluate your situation. The final decision is up to you.

I can't add further filters because PSX doesn't provide the tools that flight planning programs do. This job should be managed by external dispatch software, in my opinion. In PSX it would just lead to unwanted side effects that you'll notice two years later.


Best wishes,

|-|ardy

[simonijs]

in case an immediate landing is required and an airport above 10000 ft is the only choice, wouldn't you want to consider landing there and wouldn't you want to see that airport on the ND?

Hi,

Yes, if I could see the airport from the cockpit, during daylight and in VMC. But not when it is pitch dark, there are no charts available and the airport is surrounded by high terrain. When the suggested airport is VFR only, it may not have runway lighting.

Just tried to get into SLCN, using the VFR option to RWY10. Even with the ND at a short range terrain was showing tops at 160 not allowing further descent to the airport at 13294 ft elevation.

I agree, that the airline specific alternate airports would not include SLCN (or other airports mentioned above). But I doubt that the Honeywell FMC for the 747 will suggest alternate airports for which no charts are available.

Regards,
Simon

[Markus Vitzethum]

Hi all,

I don't know which alternate airports the FMC suggests.

However, I can comment on which airports are stored in the 747-400 FMC (legacy only, I have no data for the NG FMC.)

First of all, the airports stored in the on-board FMC database are airline specific; the Nav Database is customer tailored. Any airport stored in the database might have or might not have procedures available (SID/STAR/APP), again this is tailored.

Furthermore, for any given airport, the nav database might have runways stored (there is a seperate runway database) - or not. (If there are procedures, there have to be runways.)

So, it is quite possible that an airport shown on the ND (and available as an airport in the FMC) does have NO information whatsoever available in the FMC, not even runway information. The only information available is the location. For those airfields, you need to have charts. Obviously, these are not major airfields, but rather remote airports.

Markus

[Jeroen Hoppenbrouwers]

That list of alternates that you can uplink, is that only by simulated ACARS uplink or can you stick a text file somewhere into a PSX folder?

Hoppie

[Hardy Heinlin]

That list of alternates that you can uplink, is that only by simulated ACARS uplink or can you stick a text file somewhere into a PSX folder?

Uplink only. Accessible in PSX network.


|-|ardy

[Hardy Heinlin]

I doubt that the Honeywell FMC for the 747 will suggest alternate airports for which no charts are available.

As Markus wrote, it's not a matter of the FMC software but of the airline's nav database currently in use. As you know, the global database in PSX is not only used by the FMS simulation but also by the scenery simulation, radio models etc. which need more information than the FMS, e.g. NDB frequencies that are not displayed in the FMS and so on. Hiding NDB frequencies in the FMS, for example, is easy; that's just a single global cut. But hiding specific airports or runways is a zillion times more difficult because that needs to be tailored manually; this work would take months. As I mentioned before, PSX has no tools anyway for this work. This is manual work. And regarding the list uplink function: That's a simulation of a dispatch operation outside the FMS; obviously, the Honeywell FMC (and PSX FMC) won't uplink something to itself. This list uplink process can be overwritten by add-ons.


Regards,

|-|ardy