Alternate Airport Selection

Good afternoon forum,

When it comes to requiring an alternate I understand the 3-2-1 rule.

Visibility - 3SM
Ceilings - 2,000 AGL
Time - 1 Hours Before to 1 Hour After arrival

Then you need to file an alternate, and of course account for fuel (Fly the original airport, missed approach, hold, and re-direct to alternate)

What I am wondering on is how do you pick an alternate, is it closest airport that meets the alternate requirements? Or are some airports desigated as alternates for others, is there a formula, etc…

Thanks in advance.

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Surely there must be some pilots here with insight on this :slight_smile:

You could open the ATC menu and click the “nearest airport” option…you will then be able to request full stop landing etc

Regards
Steve

Thanks Steve,

I’m aware of that feature, and actually don’t use the ingame ATC, I use Pilot2ATC or VATSIM. My question was before even getting to that point (doing flight / fuel planning).

I know the criteria that must be met when filing an alternate is required. My question is, what is taken into consideration when choosing which airport will be the alternate.

Thanks.

No worries.
Not sure I can help you with that hopefully someone else will :+1:

Regards
Steve

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Normally you pick an alternate pre flight and take it in your calculations for flight planning. At smaller airports you might even have to call first and ask whether or not they are open and staffed to meet meet your requirements. On international airports you must make sure you could make it in time in case of night flight restrictions and so on. Big airlines have fix alternates already considered in their flight plans. By no means you wouldn’t consider any alternates at al before t/o and randomly pick one mid air. That’s for mayday only.

I mean we’re not talking about a little sightseeing trip in an ultra light right? Even in this case one or two calls made sense but…I guess you know what I mean right? :wink:

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Thanks,

Yes that is my understanding as well, what I wasn’t sure of was if there were any requirements. Meaning had to be X distrance from intended landing airport, or you just pick the closest that meets the requirements and is suitable for the aircraft you are flying.

Sounds like I would just look at the maps and pick the closests suitable airports that meet the conditions (weather wise) and then plan for fuel for those.

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Exactly. I mean haven’t you been there already it was much more than that because you had to clarify if you were even allowed to approach it. Take EDFM for example. Laws say that you’re not allowed to land there without a training with an instructor in the tower (or do you need him even on the plane? Not sure, here’s a link maybe you can translate it somehow if you don’t speak German) and you have to approach it at least once in every 6 month otherwise your license was canceled due to heavy terrain, a street crossing like 50 meters infront of the runway threshold, the runway being short, buildings are close and so on and so on. But for the sim your method is perfectly fine :+1::wink:

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Do you mean VFR or IFR?

VFR you need to be able to remain VMC of course. Depending on the airspace class it can be either 5 km and clear of clouds (visibility below 5 km to 1500 m is allowed below 140 kts or areas with low volumes of traffic) in class G (uncontrolled airports) or 5 km visibility, 1000 ft vertical separation from clouds and 1500 m horizontal for controlled aerodromes.

Thats how it is in Europe at least according part-SERA. If weather at destination is below VMC between ETA - 1 hour to ETA +1 hr you need 2 destination alternates, you need to take the fuel for the longest. Otherwise 1 destination alternate. For IFR its a bit more complex:

Weather minima take-off:

Weather minima for return to land and destination at ETD +/- 1 hr, ETA +/- 1 hr.

Normally one destination alternate is required, if weather is below landing minima two destination alternates are required.

If for take-off weather is below landing minima for return for after take-off, a take-off alternate is required.


Weather minima for alternates at ETA +/- 1 hr.

Conversion from meteorological visibility to RVR:

So to answer your question regarding alternate selection:

  1. As seen above weather plays a big part in alternate selection.
  2. Next is time, usually a non-ETOPS aircraft needs to be within one hour from a suitable aerodrome flying at the one engine out cruising speed in still air in ISA conditions. This does not mean the alternate itself needs to be within 1 hr flying as long as you remain within 1 hr flying from a suitable aerodrome at any time during the diversion, but max. 1 hr is a good aim. Take-off alternate does need to be within one hour flying with one engine-out.
  3. Next is fuel required, you could choose a far away alternate, but this would require a lot of fuel and might therefore limit the load.
  4. Terrain and obstacles might play a role as well, the aircraft needs to be able to remain clear of terrain and obstacles during diversion on one engine (engine failure is considered from the most critical point).
  5. If you fly commercially you can’t just divert anywhere you like, aerodromes need to be categorized, some airports need special training before allowed to be used. Others require a self-briefing.
  6. Landing performance needs to be checked, mostly depending on runway length and conditions. Facilities need to be sufficient, rescue and fire fighting equipment for example needs to be adequate.
  7. Last but not least, is there accomodation or other modes of transport available for stranded passengers, maintenance availability to repair the aircraft in case of failure, etc.

For example, the company I fly for supplies a flight plan for the most suitable alternate taking into account weather, operational and commercial aspects. If the weather changes suddenly there is a list of preferred alternates which I can choose from. I can then either change the plan manually, adjust the fuel etc., or call our operations and they will change it. In case none of the alternates in the list are suitable due to weather for example, I need to check the route manual what airports we are allowed to use, pick suitable alternate(s) and phone operations to change the flightplan.

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It will depend under which aviation authority you’re making the flight.

In the US, there’s no such thing as an alternate for VFR flying. Not a bad idea to have a backup plan, but even if you’ve filed a VFR flight plan (which there’s not a lot of reason to do anymore given the scope of radar coverage and flight following availibility in most places), there’s no such thing as an actual filed VFR “alternate.”

IFR, the only rules are that you must be able to fly an approach at your destination airport, fly the published missed, and fly an approach and land at your alternate with 45 mins of fuel remaining.
There are published weather mins that dictate the minimum weather required to file an airport as an alternate as well.

The choice of airport, within those constraints, often comes down to convenience. Also remember that a filed alternate is more of a dispatch requirement; you are in no way obligated to divert to that airport once airborne. If you can’t make it into your destination, you can divert anywhere you like (with a properly amended release if you’re flying 135 or 121.) There are many times in the airline world that we take off with an alternate on paper that we know we’ll never use, if we end up having to divert. It’s often just a way to get some more gas on board for the dispatcher.

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Actually there’s only one important question everybody has to consider:

“Can I somehow manage to divert to EDRG Idar-Oberstein?”

Because there you can order excellent food from their restaurant via the tower using Nato code. I heard the Sierra and Romeo was absolutely fantastic. So if you can manage to park your 747 on 2000ft of grass go for it :hamburger::fries::pizza::spaghetti::bacon::poultry_leg::wink:

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