Surprising, sometimes shocking secrets about commercial flying have been revealed by airline staff on Reddit forums and in other candid interviews and news sites. Here are some of the most interesting insights.

A Reddit user admitted that passengers who are very rude at check-in would often get allocated a seat surrounded by children. So watch your tongue if you want a quiet flight.

"Fragile" and "This way up" stickers are often not adhered to – baggage handling is a fast and physically demanding job. Instead try one that says ‘I heart baggage handlers’ suggests Reddit user fllipitinthewaistband.

It’s not customary to tip cabin crew but it’s worth it if you do – it can mean extra attention, being served first for drinks and dinner, and even a seat upgrade.

Planes are designed so that if one engine fails the aircraft won’t go down. If both engines fail the plane won’t necessarily fall from the sky either, though. Depending on the type and weight of the aircraft, most can glide for around 20 minutes, buying pilots time to arrange an emergency landing.

This is one of the few industries where you're required to sleep at work. Pilots have to sleep on long-haul flights as a safety measure (a relief crew step in to handle the plane when they do).

The oxygen masks you see in the safety videos have only around 15 minutes worth of oxygen inside. However, Reddit user jezalenko explained that it’s “more than enough time for the pilot to take us to a lower altitude where you can breathe normally.”

In the US, Federal Air Marshals are posted on certain flights to protect passengers in the event of a hijacking. They are meant to blend in with other passengers, but you can occasionally spot them in the crowd. Marshals tend to be formally dressed, well-built males sat on aisle seats (usually near the front); they don’t drink alcohol, fall asleep or engage in any entertainment; and they’ll peruse the cabin to keep an eye on other passengers.

When a plane is landing at night the lights are dimmed so passengers’ eyes have already adjusted to low light. This isn’t to help you sleep, it’s to make it easier to evacuate in case of an emergency landing.

In bad weather a hard landing isn’t caused by an inexperienced pilot; it’s deliberate, explains Reddit user Virgadays. Wet runways are slippery – a hard landing breaks through “the water layer and prevents aquaplaning.”

You know those cheap bottles of gin you thought you could sneak through customs? Well, they don’t necessarily get discarded when you get caught. US Transportation Security Administration official Jason Harrington told the Politico website that it often gets consumed by staff. You could argue it’s a perk of the job – a spokesman for London’s Gatwick Airport has firmly denied that it happens on British soil.

All manner of unusual objects have been left at airports around the world, from £50,000 signed blank checks and diamond jewellery to wedding dresses and Rolex watches. The majority is returned but anything left for more than 90 days could be auctioned off or donated.

With so many passengers daily and such quick turnarounds, planes are bound to be a bit dirty. TravelMath.com sent a microbiologist to take samples from four flights and five airports and found that the tray tables are the dirtiest part of the aircraft by far. 

They may be packaged, but the free headphones will likely have been used by a previous passenger, cleaned and then re-bagged.

Business and First Class may offer priority boarding, Champagne and a meal on china plates, but a 2012 documentary called The Plane Crash found that passengers towards the back of a plane are more likely to survive a crash.

The same documentary suggested that sitting within six rows of an exit (window or aisle; there’s little difference) also boosts your chances of survival in a crash.

High altitude and air pressure affect our ability to taste properly, and the lack of humidity dehydrates nasal passages. So while you might think your free meal is bland, you're not actually tasting the real thing. Chances are, should you eat it on land, it'll be far too salty for your grounded tastes.

The pilot will often have a First Class meal and the co-pilot a Business Class dish. This isn't because one is superior to the other, but instead to avoid both pilots getting food poisoning and being ineffective in the cockpit.

For security reasons, cabin crew can always access toilets using the latch inside the outside lock, so put away any ambitions you had for joining the mile-high club.

A Reddit user posted that passengers often fake needing a wheelchair to get priority boarding and that “10 wheelchairs get on and only one person needs it getting off. We call them miracle flights.”

According to one Reddit users, it's very common for a dead body to be stowed on board a commercial flight, and often two on bigger aircraft.

Very rarely, a section of roof or fuselage tears off (either through metal fatigue or a bomb) during a flight and decompression occurs. If you’re near the hole you can be dragged out – this happened to a member of Aloha Airline’s cabin crew in 1988 because they weren’t strapped in – another good reason to buckle up (pictured). In most incidences, however, pilots make an emergency landing with little or no loss of life.

A plane is struck by lightning bolts every two to three years, but thankfully they are remarkably well-designed to cope with a hit. The electricity is discharged by the plane’s aluminium exterior and there is rarely any damage to the surface or electrical systems.

If you arrived 15 minutes earlier than expected, don't think you've made good time. Airlines will adjust times to allow for delays, so they often look more punctual than they actually are.

According to a 2010 report ‘Specific Climate Impact of Passenger and Freight Transport’, emissions from planes have more of an impact on global warming than all the traffic on the world’s roads.

According to data on PlaneCrashInfo.com, the odds of being killed on a single airline flight (major airlines) is one in 4.7 million. You have much more chance of meeting your end while driving to or from the airport itself.

You’re a captive audience so airlines love to try and up-sell their duty free wares, but the chances are that perfume, purse or toy can be bought far cheaper online or even at the airport.