What is the Flight Management System?
What is the Flight Management System (FMS)?
In many ways, it's like the GPS in your car, with waypoints programmed in between the origin and the destination. You program in where you are going, and off it goes. The FMS will allow the airplane to hook up [that routing with] the autopilot, and maintain the heading within a few feet. It's amazingly accurate.
If I'm going to fly from New York to Los Angeles, I'm not going to just take one path in the sky, because the winds are always changing. Especially when there are big dips in the jet stream, the most direct flight path is not always the fastest or most fuel-efficient.
Where is it located in the cockpit?
The FMS is located between the first officer and the captain. Many airplanes, but not all, have two sets of input units, and you can use either one of them.
Is the FMS basically the same in all large airplanes?
Yes, it's pretty close. There are a couple of different manufactures of the system, but if you really break them down they all operate pretty closely to each other.
Who could operate the FMS in a Boeing 777?
Anyone trained on the system, so probably a commercial pilot. An aircraft mechanic might have some idea of how to use it but, at the very least, it would take someone with a pilot's knowledge of the system itself.
General Aviation (GA) GPS systems are quite similar to the FMS as well, so a GA pilot could input some information into it, but I'm not sure that a GA pilot would know what information to input. If a GPA was undisturbed, over time he or she might be able to figure that out.
When do pilots follow the FMS?
They use it for navigation almost immediately after takeoff, but the decision to fly manually versus on autopilot is up to the pilot. There are methods of hand flying the airplane that will keep it on that same course programmed into the FMS, and some pilots like to hand-fly to keep their skills up.
Quite often, the airline policy for newer generation aircraft, like Airbus and probably the 777, is to turn on the autopilot shortly after takeoff, usually at particular altitude.
Why might a pilot program a change into the FMS mid-flight?
It could be weather-related, or it could be an air traffic control directive. Certainly, if there were some sort of diversion deemed necessary by the crew, they would reprogram the FMS. Ot's just like in your car. If you were going to your aunt's house and then decided to go to your sister's house instead, you would reprogram your GPS.
I might reprogram the FMS once or twice per flight. And often in terminal areas, within 50 miles of an airport, we change runways and when we do that we often program the changes into the system.
What is the ACARS?
ACARS is a data transmission system, a method of communicating information to the dispatch center, maintenance, or to anybody who needs information from the airplane itself or from the cockpit. In layman's terms, it is way of sending text messages to people who need to know certain information.
How does it work?
Some parts are automatic and others are manual input. Lets say I'm flying toward a place where there's a thunderstorm en route, and my dispatcher may send me an ACARS text message saying, "There's a thunderstorm, consider rerouting." I'll send back a message saying, "I got it, thanks," and then I may notify the dispatch.
ACARS messages can be sent by text, but some aircraft have the ability to uplink by voice as well. The system also allows us to pull up the weather.
Where is it located in the cockpit?
Often the ACARS is co-located with the FMS, but on a different screen. It's just like using a different window on your computer screen.
Does the ACARS tell the FMS what to do?
Not at all. We can enter information from the ACARS into the FMS, but that doesn't happen automatically. The crew may be able to download position reports through ACARS, and that function could be automated in the new 777s so that the FMS could be downloaded automatically, but I'm not quite sure.
What was your reaction to the news today that the first turn that diverted MH370 from its flight path was carried out via keystrokes into the FMS?
It's interesting to me, because I don't know how they know that happened. It could be new technology that's only in the 777, but if I made keystroke entries into my FMS system on the 767, that wouldn't tell anybody on the ground anything. All I've done is change my map or my routing. When I change the plan on my screen, it's got nothing to do with what the company sees.
