http://www.gcmap.com/mapui?P=sfo-HKG+&MS=wls&DU=mi

Is the route shown in red the shortest distance San Francisco to Hong Kong?

If not, why was it chosen for the flight?

The red line was created when I entered sfo and hkg in the 'path' box and clicked Draw Map.

Thanks.

 

Edited October 13, 20196 yr by Fielder

Yes it's shortest, But

No, it's not quite the actual route

because the wind, the best route is not shortest to the ground, it changes constantly

As you can see, you might be better off by taking Track M or even Trcak J, for less headwind.

Those tarcks changes everyday

you can try it out in skyvector

Distance wise, the shortest route is going to be a straight line. When you start taking weather into consideration, that will no longer be the case. Also keep in mind that with traffic levels, a straight line isn't really viable, either. In most cases, planes will be following airways that connect waypoints and VORs.

1 hour ago, Captain Kevin said:

Distance wise, the shortest route is going to be a straight line.

? The shortest distance is the great circle distance, as shown in the above screenshot.

Which is a straight line on a curved surface......

The way the OP asked, do you belive that this was obvious to him or Captain Kevin?

https://gisgeography.com/great-circle-geodesic-line-shortest-flight-path/

Flying the rhumb line does look shorter on the map. 😉  

Edited October 13, 20196 yr by FDEdev

I'm not sure about the OP but I'm sure Captain Kevin got it. And I agree, the situation is not obvious when looking at a map......

Okay, so I had assumed that somebody who pulled up a route using the Great Circle Mapper website actually knew what a great circle route actually was, hence my original response.

Some flight`s take the safest route not the shortest, to allow for the distance from a nearby airport on route in case of emergence. 

This doesn't make sense since the likehood of a medical emergency or a technical problem increases with flight time 😉

Your example usually only applies if the aircraft is unable to fly ETOPS due to a system or equipment fault and you have to stay closer to alternate airports.

Edited October 14, 20196 yr by FDEdev

There are a couple of levels of etops certification, 120min, 180min, etc. The higher the level, the straighter your route can be direct to the destination as you always have to be within those number of minutes to a nearby alternate airport.

Its not as easy as you boys think. 

You have lots of different reasons for a routing.

1.weather 

2. The entry and exit point of your over flight permit.  As mentioned before this Is a dispatchers nightmare.  Russia, China, Mongolia, Iraq and Turkey are terrible for this.  In short you will have a waypoint on the FIR boundry that you have to route through.  You will apply for an overflight permit based on the route you want to do and either choose an allowed waypoint on the boundry of 2 Firs or have it choosen for you (it's normally the first) 

Let's take a EGLL to VHHH route for example.  Youll fly over Europe, then hit Russia, Mongolia, China, HK. 

The waypoint on the fir border between Russia and Mongolia for example might be called APPLE.  

So the point Apple is your Russia exit point for your Russian permit and your Mongolian extry point for youre Mongolia permit. 

So off you go and apply for your russia and Mongolia permit using waypoint APPLE. 

All goes well for 3 weeks until the Russian CAA tell you they are having an exercise and you cant exit via APPLE you have exit via GRAPE instead.

This now is an issue because you have to ask Mongolia if you can enter their airspace via GRAPE and not APPLE. 

So here's an example of no matter what the winds or Great circle route is on the EGLL-VHHH route you have to flightplan a certain route. 

This kind of issue happens on a daily basis for a large airline operating around the world. 

As mentioned before what we will do at my airline is we will  'prep the dispatches' so will have a template in the system for each sector.  On the template is the obvious ones like fuel contingency rules, hold times, etc etc. 

Then you will have mels to go on.  For those of you who don't what an MEL is,  it's an issue with the aircraft,  but it can still operate but you might have a restriction.  I'll explain. 

 

For example if the a/c has a fairing missing that will be a fuel penalties to go on the flight plan. That's going to effect your routing on a long routing.   But you can still operate without a fairing and you will get a date by which the fairing had to be fixed by or the aircraft can then not operate. Let's say for example 10 days.  So if your Mel starts on the 5 of January then you need to fix it by midnight on the 15th January. 

This in the business is called your 'drop dead' date.  As the aircraft 'drops dead' at midnight 10 days after you apply your MEL (the issue with the aircraft) 

Each issue that you MEL you will have a date when it needs to be fixed by.  Some are long, some are short. 

Another example of an MEL might be out of date AIRACs.  It happens.  But you can still operate on an old airac so long as the routing airways  / sid and star are the same on the new airac as on the old one. You get 10 days to fix that, or the aircraft 'drops dead' at midnight on day 10. As explained above 

Another common one is You might have a MEL related to icing for some reason.  You'll prep up a nice flightplan crossing siberia and then an engineer will tell you the aircraft is broken and you have an issue that relates to icing, you look at your flightplan for areas or icing and temperatures and you see an area you cant fly through. Great you think, back to re-dispatching it avoiding that area. 

Another MEL you might get is no Cpdlc.  This is a rare one but it happens. But you can go with a MEL with no CPDLC.  One of the restrictions is you can only use certain NAT TRACKS OR PACOTS and you have to file a constant speed and altitude on the track. 

If its a case of a 6 hour delay to fix the broken cpdlc or the above restriction you'll take the restriction. 

So all these issues, restrictions and certain overflight entry and exit waypoints are inputted into the system for all your flights and then you wait and you wait and you wait. 

Reason for the wait you ask?  its weather.  The weather / winds are released by the met office at intervals throughout the day.   

There's no point in dispatching you're flight plsn with a load of fuel penalties and other mels if you're weather is 6 hours old. Once the weather has been realeased it has go be uploaded into the lido/saber/Jeppesen servers and then downloaded onto your system 

This can take upto 3 hours,  so the 12.00z winds might not drop into your flightplanning system until 1430z. Then it's a mad rush to get you're flightplans out. 

The other example is the 1800z met office winds might not plop onto the system until 2100z then youve got a mad rush at 2100z to get out 20 transatlantic flightplans with updated weather on. Then you might have a flightplan for an aircraft with 5 mels like the icing and airac issue which you cant do anything until the weather comes up which effects your flightplan routing, which in turn effects your mels. 

Finally you have payload issues.  At commercial airlines that sell cargo you might get a last minute cargo consignment that's being trucked to the airport and then to the aircraft,  if you don't know what the exact weight is you can't update the zfw.  The systems can how many passengers and bags there is to give you an approx zero fuel weight, but last minute cargo (which is very profitable) normally you don't have the payload until the dispatcher/ground staff at the airport tells you. 

I would say the five most common things/questions  I hear at work in regards to flightplanning is 

A. 'Have you got a zfw for me please' 

B. 'hasnt this weather dropped in yet' 

C. 'what another bloody MEL' 

D.  'Why can't we go via APPLE' 

E. 'Someone tell that captain to stop calling us up, we not finished the flightplan yet, we only just got the weather' 

 

So as explained its not as easy as everyone thinks. 

 

Edited October 24, 20196 yr by fluffyflops

18 hours ago, fluffyflops said:

For example if the a/c has a fairing missing that will be a fuel penalties to go on the flight plan. That's going to effect your routing on a long routing.   But you can still operate without a fairing and you will get a date by which the fairing had to be fixed by or the aircraft can then not operate. Let's say for example 10 days.  So if your Mel starts on the 5 of January then you need to fix it by midnight on the 15th January. 

Wouldn't a missing fairing be a CDL rather than an MEL since it has a direct impact on performance?

16 hours ago, Captain Kevin said:

Wouldn't a missing fairing be a CDL rather than an MEL since it has a direct impact on performance?

it is yes., the way I always was taught is 

 

MEL - Minimum Epuipment list. -  Is all the stuff on board the aircraft.  -- ie an oxygen bottle missing , etc etc etc 

CDL- Configuration Deviation List -- is any defect outside of the normal aerodynamics of the a/c like you mentioned, a canoe fairing thats missing 

and then you have a CRAS (which i cant remember what the acromnym is) and thats a defect that isnt an MEL or CDL and is an authorisation from a part 21 company that the manufactuer agrees to/with that you can do go with,  like a large dent that doesnt fall into MEL/CDL 

I was trying to keep it simple in my post.

Edited October 25, 20196 yr by fluffyflops

Yeah, that's what I thought. You had mentioned MELs, but then proceeded to point out the missing flap fairing, which was why I got confused.