Each commercial flight in the US is required to file a flight plan before takeoff. This flight plan is created and approved by an FAA licensed dispatcher, who then tracks the progress of the flight and develops alternative routing as necessary.

An important part of the flight plan is weather conditions along the route. There are obvious safety concerns, but weather conditions are also responsible for the route chosen, the amount of fuel onboard the plane, and passenger comfort. Without weather information, the flight plan cannot be filed and the plane cannot fly. Keep in mind that there are specific regulatory standards that must be met with any information included in the flight plan. A pilot cannot simply open up the weather app on their phone for instance. The weather info needs to come from an approved source.

I have no specific information about Southwest's current issue, but my guess is the third party service they use for weather in the flight plan is out of service. If they can't transmit this info to aircraft in the air or on the ground, then nobody gets to fly today. I'm also guessing that an incident like this will result in backup solutions being put into place, and that there is an IT or systems engineer somewhere who is trying to hide their "I told you so" expression.

Edit: an example flight plan can be found here: https://www.simbrief.com/system/guide.php#ofpsample. This is from a site for sim pilots, but the format of the brief is the same as what a commercial airline would file for a flight.

I'll add to this (as a private pilot) - there are also a lot of requirements of weather at your destination; in terms of wind, visibility, temperatures and how long those forecasts are valid for and so forth.

In order to dispatch a flight you need to ensure that the weather at the arrival airport meets certain minima at that point in the future (hence the need for forecasts), and so does that at suitable alternative airports, and enough fuel is carried to be able to divert (depending on a heap of other factors such as aircraft load, capacity, prevailing winds enroute, at destination, time of day and so forth).

Aircraft are then also required to check the AWIS/ATIS or the Tower (usually the most reliable source of weather at an airfield) to ensure that the weather at the destination is within their safe margins.

There's the FAA requirements, and then airlines and aircraft and airports then also have their own established minimum requirements that all need to be within the safe range.

You can certainly dispatch a flight with potential updates and diversions as they progress / get closer to the destination, but with an outage and no means to update the enroute aircraft - there's usually no easy safe or legal way to dispatch them.

Thanks, that is certainly a plausible explanation - basically not being able to sufficiently guarantee compliance with some approved process that had a single point of failure somewhere.

I also agree that, much like when the Space Shuttle blew up, there were engineers somewhere who immediately suspected exactly how and why.

I agree with everything you wrote except "trying to hide". In these situations, it's impossible to hide "I told you so". :)

Also, the nice thing about wfh is the possibility of screaming about the stupidity of your organization more conveniently...

So if a plane is in flight (and I'm sure some were), and the weather system goes down, then what? Stick with the previous plan? Divert?

In flight weather can be observed (most airliners have weather radar onboard) and the pilots can check on weather along their route with controllers and at the destination or in specific places by electronic inquiry.

In-flight weather by radio is an option but it’s a manual thing. And the airline may not be set up to use that except an emergency situation.

It is a requirement - AWIS/ATIS and ATC/Tower (all via radio) can provide weather information at airfields, and a lot of instrument approaches do require certain readings before an approach can be commenced.

There is also the PIREPS (Pilot Reports) system where pilots report actual weather conditions as encountered by an aircraft in flight. Some aircraft have automated weather reporting systems (AMDAR).

https://www.skybrary.aero/index.php/Pilot_Report_(PIREP)

I don't think the equipment to receive weather updates is on the Minimum Equipment List, but if dispatch couldn't even update over the radio then I would imagine they would start diverting flights. This is just a guess, hopefully someone with more knowledge can jump in here.

It depends on the airframe - but I believe for Airline Transport category aircraft a storm scope and a few others are required.

I was on one of these flights, and the pilot told us that they actually had the weather information available to them on their iPad. He said the systems that failed were the ones actually creating the physical printout, which the FAA required for takeoff.

That actually makes a fair bit of sense. The FAA probably wouldn't have "safety rated" a retail iPad as meeting the primary requirement. The iPad is considered the backup but probably what they use day to day and the printout is technically the primary. So, no printout, no takeoff.

> It wasn't so long ago that pilots weather info was just a print out.

It also wasn't so long ago that scheduled domestic US airliners crashed on a fairly regular basis. That doesn't happen anymore because of advances in technology, this just being one little piece of that.

Yeah, people sometimes don't seem to understand that a lot of rules are written in blood.

Pure speculation: perhaps the FAA requirements on weather updates has changed since paper weather reports were standard?

edit: s/FFA/FAA/