Weather is a key element of the virtual world in which we fly. While flight simulator's rendition can be surprisingly rich and sometimes even beautiful, it can also occasionally be a source of frustration. A couple of pitfalls which nearly every simmer will encounter sooner or later are different weather experienced by aircraft flying on-line in the same area, and sudden changes in conditions.

Many of us enjoy the challenges of “real-world weather”, especially when flying on-line. Whatever method is used to get the weather — “VATSIM weather” through SquawkBox or FSInn, flight simulator’s built-in Real-World Weather feature or an add-on program such as Active Sky — the simulator downloads airport METAR reports from the Internet and basically uses them to make an informed guess about the conditions at the aircraft’s location. Much of the time this works well, but flight simulator can occasionally be thrown off by “duff gen”.

Sudden weather changes can occur when nearby airports report radically different weather. In the UK, METAR reports are compiled by a qualified observer. While the airport is open its METAR will be updated hourly, but when the airport closes the observer goes home and its last report becomes stale. If some of the airports flight simulator is using to generate the weather are closed but the weather has changed since, while others are open and reporting current conditions, the weather can change abruptly when flying between them.

This can sometimes be experienced on club Shoreham and Biggin nights. These two airfields close near dusk while the nearby big London airports operate till much later. Problems are worse in autumn and winter in the hours before dawn because there's a good chance of fog developing overnight: Shoreham and Biggin Hill could be reporting the clear skies that prevailed when they closed, while Gatwick could be clamped. An aircraft could take off in the clear, then suddenly enter IMC in the vicinity of Gatwick! The weather can also suddenly change when the airport re-opens at its METAR gets updated.

All we sim pilots can do is to be aware of the problem and pay careful attention when flying at times when some airports may be closed. Check the METARs for airports around the route, and if there are large differences, anticipate the possibility of sudden weather changes. The latest version of Active Sky shows a graphical map view of the weather it generates based on METAR reports, which can be used to predict conditions en route. (Flying near EGLC needs special caution at weekends — it closes for 24 hours from around noon on Saturdays, so on a Sunday morning its weather could be up to a day behind Biggin’s!)

Microsoft Flight Simulator displays the basic weather conditions that exist at the aircraft’s location everywhere; in other words, if the aircraft is currently in clear weather, clear conditions will be shown in all directions. There is no advance warning when about to enter an area of different weather! This is especially bad when the different weather area has poor visibility, because it will close in without warning. Trying to continue visual flight into IMC is a major cause of aircraft accidents among GA pilots in the real world, and can be a headache for us, too. It’s therefore worth having a plan up our sleeves to deal with this eventuality.

If we suddenly enter IMC we have a number of options, depending on our abilities and the aircraft’s equipment. Pilots without an instrument rating are trained to execute an escape manœuvre, reversing course to (hopefully) re-enter VMC as soon as possible (which always seems to take longer than it should in MSFS!). If the aircraft is IFR-equipped, we could file an IFR flight plan and continue on instruments. If we are in an aircraft like the Chipmunk with a “basic six” blind-flying panel but no nav radios and ATC is available, we could put out a PAN PAN or MAYDAY call and ask for assistance. A radar facility can give us vectors and position information to help get back into visual conditions. Some aerodromes provide a radio direction-finding service and can give us bearings. There may even be a VDF approach procedure (like at Shoreham) that can help us get down through cloud.

Different aircraft flying on-line in the same area can experience different weather when conditions are changing quickly because of different delays from when METARs are updated until they reach the simulator. For example, VATSIM weather might be updated later or earlier than the Jepessen weather information used by the MSFS Real-World weather function

Even aircraft using the same weather source, such as Active Sky, can experience different conditions such as cloud cover, perhaps due to some randomisation on the part of the weather generator or different option settings.

MSFS models “wind layers”, where different wind speeds and directions are set in altitude bands. However, it does not smooth the changes between adjacent layers. The result can be abrupt wind shifts when climbing or descending (or flying at around the border altitude between layers). Mild changes may hardly be noticeable, but greater changes can give indications like flickering airspeed indications and sudden changes in attitude and heading. In the worst case it can lead to the aircraft breaking up in flight due to overstress (as experienced by this pilot once in Alaska)! Some programs such as the payware version of FSUIPC can smooth wind changes.

Not strictly a weather generation problem. Icing can be encountered in the real-world when flying through “visible moisture” (clouds or precipitation) at temperatures at or below freezing. A few sophisticated third-party aircraft simulate ice accretion on windows and the airframe. By default MSFS does not, but it does simulate pitot tube icing if the pilot forgets to switch on the pitot heater. Unfortunately, the way it does so is totally unrealistic. With a blocked pitot tube the air speed indicator would continue to read some value, albeit a wrong one that changes with altitude. In MSFS, the airspeed indicator reading simply drops rapidly to zero! Switching on pitot heat soon restores the reading.

If the weather is too poor to fly, we can always switch the weather to “CAVOK” (not something we can do in the real world, alas!). Although viewed by purists as a cop-out, this is a legitimate action, especially when we have only limited time to indulge our hobby but when the real-world weather is simply too poor to fly. CIX VFR Club events always allow this.