ACARS - How Texting Works

Okey, texting with airplanes happens all the time. It is part of the whole process. The pilot needs to know stuff, and without tying up the air with a bunch of information the pilot may mis-interpret, or need to read later, the pilot and folks on the ground can communicate with a medium most of use use, in text.

In most aircraft, there is a keyboard and a screen up near both pilots. They have the ability to use this device to send questions to the ground, and the ground has the ability to send messages up to the pilots. Information can include weather, or flight plan changes, gate assignment. Almost anything can be sent to the pilots on the screen.

For the most part, this system works similar to a cell phone. There are ground stations all over the country. These ground stations listen on certain frequencies for a signal on a certain frequency. when these ground stations hear a message, they forward it to the assigned receiver. Each airline has assigned address(es). Delta doesn't want United hearing their messages, as much as Jet Blue doesn't want Southwest hearing their messages. Each aircraft has its' own address as well.

These ground stations are owned by various carriers, similar to cell phones. ARINC and SITA are the two major players in the world. There are some smaller carriers as well, and they are limited to certain regions in the world. The carriers don't typically inter-connect messages. If your airline is using ARINC all messages will be on ARINC equipment once they leave the operations center, until they get to the aircraft.

Different stations in the world use different frequencies so the aircraft don't overcrowd a single ground station. The ground station frequencies are similar to the VHF navigation and communication frequencies already used on the aircraft. Most of the ACARS frequencies are in the 129 to 137MHz range. Each ground station can cover about 200 miles on these frequencies.

If a pilot wants to send a message to a dispatcher in the pilot's airline operation center the pilot would tune to the nearest frequency that is on their chart, and enter the message on the keyboard. The message would get transmitted to the ground station and the carrier would forward the message to the operations center for that airline. When the dispatcher receives the message, they can enter a response. The dispatchers response will be forwarded to the carrier, and based on the last known location, the carrier will forward the message to the nearest ground station. The ground station will send the message to the aircraft.

There are a couple 'if's above. The communications protocol is quite robust, allowing for queued messages to stay queued until the ground station receives the message, and acknowledges it. If a ground station is out of service, or the aircraft is tuned to the wrong frequency, the message will sit on the aircraft, until the situation improves. If nothing else, the messages will be cleared when the aircraft power cycles itself (IE shutdown, and brought back up), no one wants to hear about something that happened yesterday.

There are automatic messages sent over ACARS as well. When the aircraft is first powered up, and the pilot initializes the computers a message will typically be sent to the operation center. This message will go into a database, and allow the airline to look at when things got started, what flight the aircraft is assigned to, and other such information. When the doors are shut, and the brakes are released an out gate time message will be sent to the operations center, and when the aircraft squat switches are showing no weight on wheels, an off ground message time is sent. The time messages that the operations center knows about and uses are called the OOOI (ooey) times, Out gate, Off ground, On ground, and In gate. There are other times, like in range that the gate wants to know about as well.

The pilots will use ACARS for many operational items. If ATC needs to divert and aircraft, the ACARS will be a way the dispatcher and the pilot can determine if there will be operational impacts to ATCs request. Will there be enough fuel to take the new route, or will the new route cause people to be delayed are all considered. If the pilot needs to know about weather ahead, some airlines have the capability to send messages to the aircraft if there are significant changes to the weather.

The ACARS unit will ding when a new message comes in. This ding is handy should the pilot be working a situation in the air, and need to know when the resources on the ground have more information. The ding can be a distraction when the pilots workload is high. Most airlines limit the ding to when the aircraft is above 10000ft. Messages can still happen when the aircraft is below 10000ft, but the ding will not distract them.

Next time you are flying, and you wonder where the pilot got all the up to date information, it probably came over the ARARS unit on the airplane.

Sequestration Ha!

I was going to write something about the furloughs and why they would cause the delays that they do, but I think everyone has heard enough. Now that they are over, it may not matter, but then again, how are they going to end...

So in a contract position, a fraction of the workforce was forced to reduce their work by 10%. Everyone is supposed be treated equal, so how can this be, not everyone had their work cut by 10%? How are they going to make it fair? The whole mess will take over a month to resolve, unless there is an emergency order, causing the folks who got the time off to be paid for the time they took off anyway (such a deal!).

I don't know if the whole deal was worked out yet. Sure congress got beat up, and something happened, but has the President signed off on it (does he need to, I am thinking he will eventually). The whole deal is a rob Peter to pay Paul anyway. No one authorized the FAA to spend what they used to spend, just that they can use some other money to pay the controllers. That money is still ready to be used for the projects it was originally intended to be used for, and someone else will be screaming if they don't get theirs.

Why do to furloughs cause delays? In a air traffic control center, there are various geographical regions that are covered, broken into sectors. Not all controllers are certified to work all sectors. The midnight shift will combine multiple sectors and work them together, where during the day, a single controller or team (RADAR (R) and Data (D) side) will work a single sector. If you don't have enough staffing, the number of controllers certified to work the sectors will be reduced.

One day the guy certified to work sectors 1,2 and 3 will have the day off, and the next day the guy certified to work sectors 2,4,6,8 will have the day off. Scheduling becomes a challenge. Then throw in vacations, and sick days, and some days you may only have one guy on a shift qualified to work sector 5 or something. For one guy to handle the sector, then only maybe 12 aircraft can be in the sector at a time. Maybe it is a gateway sector, and he is doing his best but that means that sectors 6 and 4 have to hold or slow down aircraft. Slowing aircraft has a ripple effect, and sectors 3 and 7 have to manage the aircraft coming into sectors 6 and 4 smartly (and so on).

Equipment went from same day repair to next day repair. It wasn't just the controllers on furlough, but tech support as well. If the only person who normally would be on staff certified to repair some piece of equipment was off that day, the equipment was out of commission. Maybe it was not terribly critical, but caused more inconvenience to the controller, they will have to slow even more.

So traffic backs up all day, and the airlines are taking delays. (travelers still bought tickets, and they want to get where they are going). There ends up being higher volumes of traffic at some airports until well into the midnight shift. The midnight shift that is short staffed with overlapping sectors. All the FAA can do is ask some of the night shift controllers to stay late (and pay them overtime) since the sectors will be impossibly full until even later. So everyone is taking a 10% paycut, but to make that work, the FAA has to pay overtime to some of the staff. 

Since the first week required one third to half the staff to take a day off, how is it that the other folks are going to balance that out? Again, with vacation and sick days, to make it fair, it'll probably take a month for everyone to have the same hours. I know it says that they will "fix" it by Monday, but how can that be? There were controllers who decided the whole government employment situation is silly, and took their retirement, or just quit once they got threatened with the furlough.


It kind of begs the question, who is in charge? Congress tells the FAA to cut spending, and the FAA says we can cut this or that expense, and congress says no, not that one. Why have any administrators if congress is just going to override their decisions. Tower closures were overridden. For many years the FAA has been trying to consolidate TRACONs and such to save money, but it seems someone in congress forces the FAA to not do it. Congress talks the big talk, cut, cut, cut, but when they do, they say "not that way".