Simulating Pressure Pattern flying: a resource

[connieguy]

A forum search will reveal a number of threads which refer to pressure pattern flying, the method by which aircraft used (and still use?) weather forecasts to create flight plans to take best advantage of the current winds. I have never tried it, but that is partly because I have never been able to find weather maps which were sufficiently informative. However, I have just come across the site Ventusky, and here is a screenshot taken from it:

This shows the winds very clearly and downloading the real weather with FSGRW and loading a flight plan into it shows a high degree of concurrence between the two. At a stroke one can see why routing a west bound flight from Prestwick in the UK and then stopping at Goose Bay might make more sense than doing so from Shannon and stopping at Gander. An eastbound flight would obviously be different. The time zone across the bottom is that to which your computer is set, currently GMT/UTC in my case. FSGRW uses that, but those elsewhere would need to make an adjustment.

[Defender]

That's a great find Ken. You can set wind in knots at altitudes up to 5500m and read precise forecast wind speeds with tooltips.

Bill

[Tom/CalClassic]

Actually the altitude choices go up to 30,000 m if you scroll the menu list down. But I agree, great resource!

[Defender]

As an example, here are the Ventusky winds at 5500m at midday today. Where the jetstream was today you could do LAX to London non-stop but not by the "polar" route. The winds would make the great circle route impossible without a fuel stop.

But the southerly route on the FSNavigator chart below would today give tailwinds at 17,000' or 19,000' averaging at least 75kts all the way, 100kts or so over the mid-USA. Even if the northerly route had a more typical 25kts average tailwind, a DC-7C taking today's southerly route, despite being about 600nm longer, would arrive at least 30 minutes earlier. 
 




Of course the 1950's planners did not have forecasts as accurate as this but they would have had pressure charts updated from weather ship and aircraft reports, and your navigator would use his radio altimeter, drift and ground speeds calculations to check the accuracy of the forecasts.


Bill 

[Tom/CalClassic]

Bill, I thought about that exact route when I first brought it up! That is one of the most obvious examples where pressure pattern flying can be very useful.

The opposite is true when flying the route westbound - you want to head north of Prestwick, then cross over Frobisher Bay (north of Hudson Bay), stay in northern Canada, turn southeast at the Rockies, and then fly down the west coast to LA.

[Tom/CalClassic]

A 1954 Google book on the topic, but it is quite detailed and not an "easy how to" book.

books.google.com/books?id=FqoYo0e9XX8C&pg=PA62&lpg=PA62&dq=pressure+pattern+flight+planner&source=bl&ots=mppVCMqFVX&sig=ACfU3U1u971sF6-a4iLbpI9wA7tfydN3uQ&hl=en&sa=X&ved=2ahUKEwiPwsK1uYf1AhXEKs0KHeVkDUk4ChDoAXoECBIQAw#v=onepage&q=pressure%20pattern%20flight%20planner&f=false

[Tom/CalClassic]

Hi,

I flew a Pan American DC-7C from LAX to London, following the "atmospheric river" that is present now. LAX-ABQ-OKC-STL-IND-PIT-NYC-East to N40*41' W41*58'-Cork-EGLL. After I got above 12,000 ft I caught tailwinds. I eventually got up to 18,000 ft. I had tailwinds between 45-90 kts for most of the way. I landed with less than normal reserves, though! I departed at 11 am and arrived at 1:35 pm (the next day), 45 minutes early.

At least I found out how to manually add waypoints to my FS flight plan.

[Tom/CalClassic]

I was thinking about my fuel reserves. I did use up my headwind reserve, but that was during the last part of the flight and I still had tailwinds predicted the rest of the way (using Ventusky) so that was OK. Then once I got to Ireland I could have checked on London weather and found it to be clear, so I could dispense with the diversion reserve (2040 lbs). Then as I was making my approach to the airport I found there was no holding (another 2040 lbs), so then it was only how much minimum fuel my airline required upon landing. I don’t know about Pan Am, but Eastern DC-7Bs required 500 gallons (3000 lbs). This is probably where I stretched things a little too far - I only had 2400 lbs when I landed.

[Defender]

Glad to hear you managed to try out that route Tom. Sadly I haven't had enough free time this week.

The Pan American manual has a very detailed section on planning and reserves. I suspect on this type of flight you might use two or even three consecutive flight plans, initially planning to say Lajes in the Azores, alternate Santa Maria, even if intending to track well north of that, then cancelling mid-ocean and re-filing to London either as intended or as alternate, thus taking advantage of the lower reserve levels needed. Or initially also planning only as far as New York and cancelling en route.

The CAR rules are strangely generous on fuel requirements,

"In computing the fuel required for an
airplane, consideration shall be given to
the wind and other weather conditions
forecast, traffic delays anticipated, an
instrument approach and possible missed
approach at destination, and any other
conditions which might delay the land -
ing of the airplane",

so it seems to allow you to factor in any tailwind forecast that the weather office makes available and ignore any headwind factor.

Bill

[Tom/CalClassic]

I think it says the opposite?
"In computing the fuel required for an
airplane, consideration shall be given to
the wind and other weather conditions
forecast... which might delay the land -
ing of the airplane".

But you are right, I know they would file an initial flight plan for a closer destination and then refile later if conditions were OK for a longer or even non-stop flight. That said, it was pretty typical for DC-7Cs to stop somewhere on polar flights. I bet the passengers would have been confused if I had stopped at New York for fuel!

[Defender]

Tom,

How did you create your waypoints? There are two useful features in FSNavigator. FSNav shows an named intersection at each degree of longitude and latitude, e.g. 35N40W.Then if you want to create an FS9 flight plan and navigation log, FSNav allows you to place a "fix" at the position of any historic beacon, intersection or reporting point that you know the location coordinates of and you can export that plan to FS9. If you then open that new FS9 plan with notepad, each "fix" can be renamed with its actual name, up to ten letters, and that is how it will appear in your FS9 navigation log.

Here's how the flightplan looks for the American Airlines DC-7 Mercury flight on YouTube, Idlewild to Los Angeles.

[flightplan]
title=KJFK to KLAX
description=KJFK, KLAX
type=IFR
routetype=1
cruising_altitude=20000
departure_id=KJFK, N40* 38.39', W73* 46.74', +000013.12
departure_position=13L
destination_id=KLAX, N33* 56.55', W118* 24.48', +000124.67
departure_name=Kennedy Intl
destination_name=Los Angeles Intl
waypoint.0=KJFK, A, N40* 38.39', W73* 46.74', +000013.12,
waypoint.1=1200 ft, I, N40* 36.20', W73* 40.25', +000000.00,
waypoint.2=Mitchel, I, N40* 43.20', W73* 34.53', +000000.00,
waypoint.3=GlenCove, I, N40* 50.42', W73* 37.07', +000000.00,
waypoint.4=UR, N, N40* 51.99', W73* 48.21', +000000.00,
waypoint.5=Branchville, I, N41* 13.45', W74* 35.96', +000000.00,
waypoint.6=ScrantonE, I, N41* 25.57', W75* 3.32', +000000.00,
waypoint.7=WI, N, N41* 20.10', W75* 46.61', +000000.00,
waypoint.8=SEG, V, N40* 47.45', W76* 53.04', +000000.00,
waypoint.9=PSB, V, N40* 54.98', W77* 59.56', +000000.00,
waypoint.10=Brookville, I, N41* 9.02', W79* 6.01', +000000.00,
waypoint.11=Mars, I, N40* 42.00', W79* 56.06', +000000.00,
waypoint.12=LaFayette, N, N40* 25.61', W87* 3.11', +000000.00,
waypoint.13=IRK, V, N40* 8.10', W92* 35.50', +000000.00,
waypoint.14=CNK, N, N39* 33.20', W97* 39.07', +000000.00,
waypoint.15=PUB, N, N38* 14.67', W104* 30.09', +000000.00,
waypoint.16=CEZ, V, N37* 23.39', W108* 33.71', +000000.00,
waypoint.17=BlackMesa, I, N36* 52.66', W110* 28.85', +000000.00,
waypoint.18=LakeMohave, I, N35* 36.03', W114* 39.09', +000000.00,
waypoint.19=DG, N, N34* 51.01', W116* 50.00', +000000.00,
waypoint.20=FONTA, I, N34* 3.38', W117* 28.29', +000000.00,
waypoint.21=PDZ, V, N33* 55.11', W117* 31.80', +000000.00,
waypoint.22=LAHAB, I, N33* 55.54', W117* 55.55', +000000.00,
waypoint.23=LA, N, N33* 57.03', W118* 16.55', +000000.00,
waypoint.24=AX, N, N33* 56.44', W118* 22.41', +000000.00,
waypoint.25=KLAX, A, N33* 56.55', W118* 24.48', +000124.67,

The navigation log then adds the heading and distance between each point, although only FSNav will lock the autopilot to follow the route itself.  

Bill

[connieguy]

I have not been as adventurous as this, but I have done the Prestwick - Goose Bay route in a C-121, with the weather of 24th-25th December, 2021. The route was the direct great circle one, with waypoints along it partly to provide weather forecast points and also coordinates for sextant shots. The FSGRW weather report suggested I would have tailwinds of about 50 knots. I cruised at FL120, 160 and eventually 200 (at a gross weight of 118,000 lbs). Not for nothing did Pan Am tell navigators that they should take at least one sextant shot a trip to keep in practice, because I haven't done it for some time and was rusty. The first one showed me to be well south of the track. Then the clouds closed in and no further shots were possible for two hours. In the meantime I adjusted the heading to what I guessed would be about right and then corrected it when I guessed I was about back on track. When the next sextant shot came I was just north of it. One thing that made this easier was that with tailwinds there is very little drift. Not too long after that I picked up Ocean Station Baker/Bravo and navigationally that was it. There was a tricky landing in a visibility of 2 nm at Goose Bay, but that is a less creditable story.

[Tom/CalClassic]

Hi,

Bill, I just used Notepad to add the waypoint in the middle of the ocean. Here was my plan:

[flightplan]
title=KLAX to EGLL
description=KLAX, EGLL
type=VFR
routetype=0
cruising_altitude=17500
departure_id=KLAX, N33* 56.84', W118* 24.30', +000125.99
departure_position=GATE I 55
destination_id=EGLL, N51* 28.56', W0* 25.96', +000080.00
departure_name=Los Angeles Intl
destination_name=London Airport
waypoint.0=, KLAX, , KLAX, A, N33* 56.84', W118* 24.30', +000125.99,
waypoint.1=K2, PSP, , PSP, V, N33* 52.20', W116* 25.79', +001600.00,
waypoint.2=K2, PKE, , PKE, V, N34* 6.12', W114* 40.92', +001000.00,
waypoint.3=K2, DRK, , DRK, V, N34* 42.15', W112* 28.82', +004962.99,
waypoint.4=K2, ZUN, , ZUN, V, N34* 57.95', W109* 9.27', +006549.99,
waypoint.5=K2, ABQ, , ABQ, V, N35* 2.63', W106* 48.98', +005739.99,
waypoint.6=K4, PNH, , PNH, V, N35* 14.10', W101* 41.94', +003591.99,
waypoint.7=K4, IRW, , IRW, V, N35* 21.52', W97* 36.55', +001230.00,
waypoint.8=K4, TUL, , TUL, V, N36* 11.78', W95* 47.29', +000790.00,
waypoint.9=K3, SGF, , SGF, V, N37* 21.36', W93* 20.04', +001240.00,
waypoint.10=K3, STL, , STL, V, N38* 51.64', W90* 28.94', +000450.00,
waypoint.11=K5, VHP, , VHP, V, N39* 48.88', W86* 22.05', +000870.00,
waypoint.12=K5, APE, , APE, V, N40* 9.06', W82* 35.30', +001350.00,
waypoint.13=K6, EWC, , EWC, V, N40* 49.51', W80* 12.69', +001220.00,
waypoint.14=K6, SAX, , SAX, V, N41* 4.05', W74* 32.30', +001410.00,
waypoint.15=K6, ACK, , ACK, V, N41* 16.91', W70* 1.60', +000100.00,
waypoint.16=, N40W41, , N40W41, I, N40* 41.00', W41* 58.00', +000000.00,
waypoint.17=EI, CRK, , CRK, V, N51* 50.44', W8* 29.66', +000500.00,
waypoint.18=EG, HDW, , HDW, V, N51* 49.93', W4* 58.18', +000200.00,
waypoint.19=EG, FFA, , FFA, V, N51* 40.83', W1* 47.99', +000299.00,
waypoint.20=EG, LON, , LON, V, N51* 29.23', W0* 28.00', +000110.00,
waypoint.21=, EGLL, , EGLL, A, N51* 28.56', W0* 25.96', +000080.00,

I just added waypoint.16 by hand in Notepad, based on a forum thread I read (actually I copied and pasted the CRK waypoint back into the file, then edited the new line). I then renumbered the waypoints after that. Works fine.

And plans created and loaded by the Flight Planner can be flown by the AP in Range mode with the GPS/NAV switch thrown to GPS - I did just that since this was a flight testing the winds, not my navigation.

But I do have FSNavigator installed, and often use that for my real flights - I just wanted to know if it was possible without it.

[Defender]

Thanks for the flight plan explanation Tom. So not only can we rename waypoints, we can add to them following the text format.

Re reserves, I agree that the reference to wind is in conjunction with delay but there is nothing to say that tailwind is not to be taken into account. The Pan American flight planning charts do show an allowance for tailwinds but slightly less than would be added for the same wind speed as a headwind. And of course too much route fuel could cause excessive landing weight problems. I'm not sure I would use up my alternate reserve before landing. It's not just weather that could shut down a runway or even an airport, although of course aircraft do divert with nothing left for a further diversion.

Bill

[Tom/CalClassic]

Thanks. I assume that is one reason Eastern insists on a minimum fuel load upon landing, no matter what. You just never know...

My diversion reserve was 2040 lbs and I landed with 2400 lbs, so I was actually OK there.