Malaysia Airlines Flight 370—Understanding Terminology

Over a week and a half have gone by since Malaysia Airlines flight 370 was last seen flying at 35,000 feet above the Gulf of Thailand on its way from Kuala Lumpur to Beijing. Dozens of ships, airplanes, helicopers, and satellites are currently searching thousands of square miles of sea and land to find MH370, but have so far come up empty. Perhaps most maddening is that we still have no idea what happened. The bits of information that have trickled out since it disappeared haven’t really brought us any closer to understanding where MH370 is and what happened on board.

The past week and half have been a steep learning curve, especially for those who don’t normally follow aviation. Navigating the jargon of the business can be confusing and separating all the acronyms can get in the way of understanding the situation.

What this post is: an attempt to put together some pieces of information so that reading the news doesn’t mean looking up a new acronym every two words. If you’re confused at all by ACARS vs TCAS, or you think ADS-B is what kicks in when your car hits a patch of ice, this post should shed a little light and I’ll do my best to update this post with answers to any questions you may have.

What this post isn’t: a compendium of theories of what happened to flight 370. If you’re looking for that, there are plenty of other places willing to entertain wild speculation.

So what are we talking about?

What kind of plane is it?

Malaysia Airlines Flight 370 is a Boeing 777-200ER, registered 9M-MRO, pictured below. The 777-200ER has a range of 7,725 nautical miles and can carry over 45,000 gallons of fuel. This particular aircraft is powered by Rolls Royce Trent 895 engines.


Primary vs. Secondary RADAR? And what’s ADS-B?

We’ve heard a lot about primary and secondary radar—and transponders, but more on that below—this week, but isn’t radar just radar? Not quite. Primary radar is what most people think of when they hear radar. Primary radar sends microwaves out and waits for them to bounce back telling the radar station that an object exists and its distance from the radar station. Secondary radar provides aviators and air traffic controllers with a much more precise way to monitor aircraft. Secondary radar sends a signal to a plane that is equipped with a transponder, which receives and interprets the signal and then sends a corresponding signal back to the radar installation with information about the plane’s position. ADS-B (Automatic Dependent Surveillance-Broadcast) is a newer system takes this a step further. Planes equipped with ADS-B determine their own position via satellites and then broadcast that information to air traffic control and other aircraft. Websites like FlightRadar24 and Planefinder compile ADS-B data from aircraft and provide for real-time tracking of flights. The data generated by ADS-B is what much of the original discussion of MH370’s disappearance revolved around.

Update March 18, 9:40amCT: Here’s a great article by AP’s Scott Mayerowitz and Joan Lowy on why airplane transponders have an off switch.

A screen capture from FlightRadar24 showing the last broadcast position of MH370.

A screen capture from FlightRadar24 showing the last broadcast position of MH370.

What is ACARS?

ACARS or Aircraft Communications Addressing and Reporting System allows aircraft and ground stations to communicate short messages via radio frequency or satellite. These short messages can be related to air traffic control—such as a new route, or to maintenance—the airplane automatically telling the airline that the engine needs to be checked upon landing, or to something more general, like the weather ahead.

What are “Satellite Pings?”

Tim Farrar of TMF Associates, a firm specializes in satellite communications, provides an excellent and detailed overview of the satellite pings on the TMF Associates blog. MH370’s onboard terminal contacted an Inmarsat-3 satellite roughly every hour allowing investigators to construct the two possible arcs where MH370 could be.

Two possible arcs on which MH370 may reside. Image source.

Two possible arcs on which MH370 may reside. Image source/WSJ.

MH370 pinged the Inmarsat-3 satellite orbiting over the Indian Ocean (the blue satellite in the image below).

Coverage of the Inmarsat-3 satellite network. Image source, courtesy Inmarsat.

Coverage of the Inmarsat-3 satellite network. Image source, courtesy Inmarsat.

Now what is this TCAS I’m hearing about?

TCAS—Traffic Collision Avoidance System—is the most plainly named system here. TCAS is designed to do exactly what it says: avoid collisions. TCAS uses the plane’s transponder to monitor other aircraft in the area and warn pilots of any danger of collision.

Are satellite pings different than locater pings? What is a underwater locator beacon?

The underwater locator beacon pings and the earlier satellite pings are different. Attached to ever airplane’s black box is an underwater locator beacon—also known as an underwater acoustic beacon—that emits an acoustic pulse when immersed in fresh or saltwater. Once submerged the beacon emits one ping per second. The beacons are designed to withstand immense pressures and can operate for 30 days at a depth of 20,000 feet under water. When wreckage is found specialized equipment like the U.S. Navy’s Towed Ping Locator 25 can be used to detect the beacon’s pings and the airplane’s black boxes.

Underwater Locator Beacon

A example Underwater Locator Beacon, similar to the one on MH 370. Image courtesy Wikimedia Commons.

So now, when you’re watching the news or scrolling through twitter, you’ll have a bit of an idea of what is being discussed. What else would you like to know? Let me know in comments and I’ll do by best to answer your questions.


Header image used under Creative Commons license from Flickr user Schiefi

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