As we go into another day wondering where Malaysian Airlines MH370 is, the biggest question is: how does such a big airplane vanish with no apparent trace? But first we need to understand how airplanes are tracked today.
The 777 is one of Boeing’s most advanced aircraft with some of the most up-to-date communication equipment on board. There are four primary methods of communication with an airplane. The first is the standard method of radio communication. This is where the pilot informs air traffic control of his position and altitude verbally.
The second method of communication is via radar, in this category there are two types. The first is primary radar, this is simply the radio reflection of the airplane (sort of like the way a flashlight lights up an object in a dark room). While the commercial version of this first type of radar may tell you how far an airplane is from the ground station, it does not convey altitude or airspeed, for this secondary radar is used. Secondary radar sends a signal to the airplane asking it for more information. Since the direction from which the signal was sent is known, the general direction of where the airplane is is also known. When the airplane’s onboard transponder sends back information (altitude, airspeed, etc) then the complete picture is displayed on the air traffic controller screen (ATC): position, altitude, and airspeed.
The third method of communication is starting to become more mainstream and will become required by the FAA by 2020. This is called Automatic Dependent Surveillance-Broadcast (ADS-B). With ADS-B, more information is transmitted back to the ground station and does not depend on ground-based stations for receiving/transmitting data. It is connected via satellite to any necessary ground station. The benefits of this are obvious when we look at flight MH370 and a bit further back at Air France 447. With AF477 it was not known that the flight had a catastrophic event until at least 2 hours later, when it was supposed to be flying over Senegal. The reason for this is that flights routinely “vanish” from their digital tracks. When a flight leaves a radar-controlled space, say, flying across the Atlantic where there is no real-time radar tracking, the flight’s last known position, airspeed, and planned flight path are used to predict its progression along its route. When the flight arrives again at a radar controlled zone it is supposed to check in. In AF477’s case, when the first ATC failed to get an acknowledgment from the flight’s pilots, he assumed they either did not hear him or they were busy. It was only when a later ATC in Senegal looked further into the matter (when he, too, failed to get an acknowledgment) that it was discovered that AF477 had had a catastrophic event. This is something the ADS-B would remedy. Even with a transmission rate of once per 30 minutes, it would still offer far greater accuracy to determine where a flight truly is.
The last method of communication between the ground and an aircraft is something called Aircraft Communications Addressing and Reporting System (ACARS). ACARS is a text-based system that allows the airplane and pilots to send information to the aircraft manufacture and airlines headquarters to report anything from routine maintenance issues to possible weather alerts along the flight path. The ACARS can also be used as a kind of “are you alive” signal since it apparently can not be turned off. In the MH370’s case it is this signal that has led investigators to believe that the plane flew for more than 5 hours after all other forms of flight tracking were turned off since this signal was repeatedly received hourly between 4 and 6 times after the flight vanished.
With all these communication systems in place one would think that it would be difficult for a plane to completely disappear. According to the current assumed flight path, it is thought that the plane flew back over Malaysia and possibly over mainland Asia. So how does a plane just disappear? Even if all onboard systems could be turned off, couldn’t radar track it since the plane was apparently flying over land and in some cases even through militarized areas?
Let’s start with the onboard communication devices: the transponder, the radio and the ADS-B. These can all be turned off, except for the ACARS. Far from being bad design, this is a necessary safety requirement. In the event of a short circuit that could lead to a fire all systems on board need to have the ability to be shut down. So if the onboard systems were turned off why did no one notice? The answer to this is based on how flights are tracked when out of range of radar. Above it was explained that when a flight leaves a radar-controlled zone it is tracked virtually, that its last known position, airspeed, altitude and flight plan are used to predict where it is at any given moment. This projection is used until the aircraft arrives back in a radar-controlled zone.
OK, so all major tracking systems are turned off,. But why can't they see the flight on radar? The answer here is one that might be a bit surprising. In civilian air traffic control towers, most controllers turn off the primary radar reflection to remove clutter. Clutter like: birds, clouds-- anything that the radar picks up but may not necessarily be an airplane. So to get a clearer picture of what is really important, air traffic controllers turn off the primary image and leave the secondary image, which displays all confirmed flights in the area. This does not, however, mean that military installations in the area won't see you. But in Malaysia, India and other countries in the area, military radar is only turned on when there is a good reason, such as a perceived threat. There is also the possibility that someone with knowledge could fly around or under military radar. The aircraft would need to fly under 5000 feet to pull this off-- no simple task, but also not impossible.
So now that we have evaded both civilian and military radar operators, what do we do with the plane? This is one of the bigger issues with this theory, but even this is not impossible to speculate about. In an emergency, the Boeing 777 has the ability to land on a relatively small runway that may or may not be paved. It has been stated that even a well-packed dirt runway could potentially be used. For someone that has worked out how to get a plane this far, getting it on the ground would hardly be a difficult task.
The real frightening question is with a plane full of people on a remote air strip somewere, what do you do with these people? I hope and pray that nothing barbaric or inhumane took place.
Now that we have a potential scenario of how a plane just vanishes, how do investigators have any idea where the plane may be? This is where the ACARS has proven useful. It reports back to the plane manufacturer on routine maintenance issues as well as engine operating conditions. This information is used to monitor the health of an aircraft even before it is brought in for inspection. Although this is a paid service and not all airlines use it (Malaysian Airlines apparently does not pay for this service) it is still a useful system. It’s the same reason many cell phones work both in their immediate service area, and also in new areas: phones respond to requests for information even if the request comes from a different service provider. In the case of the ACARS the system sends out a ping to all radios even if that particular plane is not subscribed to the service. The onboard system then responds with an acknowledgement of the ping. It is this information that investigators have used to give a radius of where the flight may have ended up. This is calculated by taking how long it took from the time the signal was sent out to the time the acknowledgment was received, half of this time is the distance to the airplane. The limitation with this is that it still gives a very large search area-- tens of thousands of miles-- even if remaining flight time is taken into account based on available fuel. We’re still talking about a vast area.
So how can we use this information to prevent a plane from vanishing in future? I believe the ACARS system is the answer to preventing planes from vanishing. When a plane responds to a remote ping, it must reply in a standard format. Adding a few more fields to the message would add very little overhead and cost to the existing system, and could provide GPS location information of the flight. This would narrow a search from hundreds of thousands of square miles down to hundreds of square miles. In the case of flight MH370, it would have told us where the plane had been over its last 5 hours of flight, which would have significantly reduced its current search radius.
What do you think? I’d love to know what you think could help improve aircraft location technology. Post your thoughts below in the comments.
