AIRCRAFT stowaways enjoy a free plane ride, but the big catch is that they may not get to their destinations alive.
They risk freezing temperatures, suffocation, being crushed or falling to their deaths - crouched as they usually are in the plane's wheel well.
The danger to their lives aside, stowaways - and there have been two in the last two months on Singapore Airlines (SIA) planes - have put the focus on airports' ground security.
Aviation experts say stowaways generally pose no security threat to aircraft, but the fact that they have been able to gain access to planes means there are loopholes in security around aircraft and airport perimeters - loopholes which can be exploited for ill intent.
That the second of the two incidents involved a cargo plane also raises questions about their security, generally less stringent than for passenger planes.
Last month, a Palestinian man fell out of the nose wheel well of an SIA passenger plane at Changi Airport after the plane arrived from Kuala Lumpur.
Charges against him were dropped here and in Malaysia but he could still be charged by the Palestinian government when he returns there.
Then, earlier this month, in the incident involving a cargo plane, a man believed to be an Indian national was found in one of six passenger seats an hour into the seven-hour flight from the Middle East to the Netherlands. He is believed to be still under investigation in Sharjah in the United Arab Emirates.
When contacted, SIA spokesman Stephen Forshaw said these incidents underscored the need for airlines to work with the airport authorities to strengthen security surrounding airports and aircraft.
He told The Straits Times: 'The acceptable goal must be that no person can gain access to an aircraft without first, appropriate documentation, and second, access screening.'
Aviation experts say the security of an aircraft is only as good as the airport out of which it operates, and airlines do not have much control over this.
Stowaways typically try to grab on to an aircraft's wheel as it is taking off. Once the plane is airborne and the wheels retract, they find themselves in the wheel well.
There have been 75 stowaway attempts on 65 flights worldwide since 1947, said the United States' Federal Aviation Administration this year. Of these attempts, 59 ended in death.
When stowaways - many of whom are fleeing poverty, oppression or the law - are found out, the plane has to turn back, which means flight delays.
While stowaways should face the music, getting through security is not in itself a crime, unless some form of deception, like identity fraud, was employed, said Mr David Learmount, operations and safety editor of authoritative aviation magazine Flight International.
Experts agree that airports and airlines are to blame for security breaches - but they get off too lightly for this, said aviation security editor Chris Yates of Jane's Information Group, an authoritative intelligence provider.
He said: 'Perhaps if they were penalised heavily for having such lax security as to allow such occurrences to happen, then we would see a corresponding improvement in security at our airports and a downturn in the number of attempts to stow away.'
But until then, one of the most immediate ways to enhance security of cargo planes is to install cockpit doors to protect the pilots, say experts.
Passenger planes now have them, but such doors are not mandatory for cargo planes.
Air Line Pilots Association-Singapore president Captain P. James agreed that installing such doors would improve the security of cargo planes, but stressed that the bigger issue was how airports provide security for both passenger and cargo planes.
The Straits Times understands that SIA is in talks with aircraft manufacturer Boeing to install cockpit doors in its cargo planes. Both parties declined comment when asked, citing security reasons.