To answer that, yes, an airplane can get hacked. There have alerts issued by the U.S. feds for possible hacking of aircrafts. There are only two possible ways of hacking to disrupt a flight on its course;
(a)To hack onto the transmission where the hacker could potentially disrupt electronic messages so as to misguide the aircraft or,
(b)To hack into the central computer of the system of the aircraft where the hacker could disrupt the functioning by inserting a malware.
Either ways are as simple as it sounds, if a hacker can with sheer ease transact money from the Reverse Bank of India right under its nose, without any alert from their firewall, so can it be done to discourse an aircraft from its desired destination or to crash it, killing everyone on board. The gravity of such a crime is ominous as the lives of people are at stake and a secure system will be required avoid such events.
An incident in the year 2008, crash of Spanair Flight which crashed just after taking off from the Barcelona–El Prat Airport and killed more than 150 people who were on board the aircraft and the conclusion post investigation was that someone used the central computer system to monitor the technical problems within the aircraft and feed a malware into it. They also discovered that if the systems were advanced and maintained enough they would have able to detect the internal failure beforehand the aircraft might have not taken off in the first place. Such an incident is proof that a cybercrime such as hacking does not only stop at breaching and corrupting your personal data but also to take lives which are usually matter of terrorist activities.
It certainly is possible but not easy. There are a few requirements that are needed for someone to hack into an aircraft’s system. There should be a physical access to hack into their system, it may be through the media controller used by the passengers during course of flight, it may be through the access of Wi-Fi through some passenger doing video calls , any messenger service or even a web link. Any small door to the system can efficiently allow hacking into the system. To show how convenient it has become, US Department of Homeland Security official hacked into the systems of a Boeing 757 passenger aircraft parked in the airport in Atlantic City, New Jersey. He stated that such an invasion was a remote, non-co-operative penetration. He had done this without getting any physical access into the aircraft’s system or using devices that infect malware. Then thereon the US Department of Homeland Security issued an official hacking alert especially for small planes. The wider the interconnectivity of the devices the more vulnerable are the systems near them, which includes the plane. A report of 2006 shows a number of 50 GPS interferences at the Manila International Airport which were forcing of landing of aircrafts during congestion on the runway by re-navigating the route.
The vulnerabilities are not so big as of today, but may grow eventually and waiting around to give such an open window to criminals is a failure of our security that lets cyber-criminals or terrorist based hackers to get their way into our systems and not only take data, but lives.