Some airlines equip their planes with body bags, just in case.
Singapore Airlines' fleet of Airbus A340-500 aircraft, which were used on all-business class flights to the US and are no longer in service, became the first to include a so-called 'corpse cupboard', a discreet locker large enough to store an average-sized body.
While a 'corpse cupboard' may sound extreme, staff are trained to move a deceased passenger out of view from other travellers.
But that is not always possible, depending on the number of passengers on board and the size of the plane.
If there is no space, cabin crew are told to cover the person with a blanket up to their neck and tighten their safety belt.
If a death occurs shortly after take-off it could result in a plane returning to its airport of departure, while unscheduled landings have occurred in rare cases where a passenger died in-flight.
A recent BBC2 documentary, titled A Very British Airline, revealed how British Airways trains its cabin crew to respond when a passenger dies.
New recruits were told they cannot place a dead passenger in the loo because the passenger could slip off the seat and wind up on the floor.
The trainer said: 'You would have to take the aircraft apart to get that person out. Imagine putting someone in the aircraft toilet.'
A British Airways spokesman told MailOnline Travel: 'We expect our cabin crew to treat customers who have passed away with dignity and respect.
'This usually involves trying to move the person to an available seat in the most private area possible.
'Our cabin crew will then focus their efforts on looking after any family, friends and travelling companions to give them privacy and support at an extremely stressful and upsetting time.'
But finding a possible area is not always possible on planes which are not configured with first or business classes.
Space is at a premium on flights offered by Ryanair, Europe's largest budget airline.
A spokeswoman for the Dublin-based carrier said its planes will make an unscheduled landing if it is a medical emergency.
She said: 'All of our crews are trained in first aid. Should an incident occur in flight which requires medical intervention, our crew will ascertain whether any medically trained individuals are on board and divert to the nearest suitable airport, requesting medical assistance to be on standby before landing.'
A spokesperson for Qantas, Australia's national airline, said deaths on its planes are 'very rare'.
The spokesperson added: 'If a passenger passes away during flight, our cabin crew are trained to handle the situation with the utmost respect and dignity.'
Carolyn Paddock, a former commercial flight attendant who continues to fly for a private client, said an in-flight death is a 'terrible thing' for everyone on board.
She told MailOnline Travel: 'Each person is going to handle it differently. That said, in my experience cabin crew are incredibly tenacious and resilient people who have incredible stamina for experiencing all sorts of crazy and upsetting events and being able to move through it, carry on, and ultimately be OK.'
In many cases, the plane continues to its destination.
Carolyn added: 'It's determined case by case and it really depends where in the world you are - and how will it impact the passengers.
'For example, are you flying over the middle of the Atlantic? A lot depends on where you are and where your destination is.
'It may be most beneficial to continue to your destination because landing prematurely will cost the airline and passengers quite a lot of money and incur missed connections, fees, and more.'
Last December a 23-year-old woman from New Jersey died on a transatlantic flight from London to Newark Liberty International Airport, near New York.
A doctor who was on board attended to the woman and tried to resuscitate her, but she was declared dead.
The plane continued its journey and was met by police officers and a medical examiner when it landed in Newark.
In some cases, passengers are not allowed to disembark until authorities board the plane, inspect the body and conduct interviews.
In 2007, a woman in her 70s was moved to the first class cabin from economy after she died on a British Airways flight from New Delhi to London Heathrow.
One of the passengers was asleep and woke up to find cabin crew putting the woman in his row, where she was propped up using pillows in a seat next.
For the next five hours, the women's body rested in a seat next to her grieving daughter and son-in-law.
Passenger Paul Trinder told The Times: 'She kept slipping under the seatbelt and moving about with the motion of the plane. When I asked what was going on I was shocked to hear she was dead.'
Some passengers were questioned when the plane landed.
Airline employees are also trained to deal with deaths involving their colleagues.
Although incredibly rare, one such situation occurred in 2009 when a 60-year-old Continental Airlines pilot died from a heart attack while flying from Brussels to Newark.
Two co-pilots safely landed the plane in Newark, and officials said the 247 passengers were not in danger.
