It’s a truth that frequent flyers hear time and again and probably take for granted, but your airplane ride might just be the safest part of your day.

Last year was the safest year ever for commercial aviation, Aviation Safety Network data shows, and the average yearly number of aviation fatalities has been falling steadily since 1997. It’s all thanks to the continuing safety-driven efforts by international aviation organisations, and the evolving technology and design of modern aircraft.

Since the dawning of commercial airliners, more than 50 years ago, more than one billion flight hours have been wracked up. This accumulation of experience and information have given airlines, designers and manufacturers the insight needed to make constant improvements to the design of aircraft.

Every detail of your plane, from the cockpit and wings to cushion covers and floor plan, has been carefully considered with safety in mind. Even if you fly all the time, you may be surprised by just how many safety features are hidden in plain sight, and the little details you never even knew existed.

The next time you board a flight, you may want to pay closer attention. Here are the hidden safety features that can not only make your journey more comfortable, but might make all the difference in the unlikely event of an emergency situation.

23 18. Hidden in plain sight: This Is Why Airplanes Still Have Ashtrays

Smoking is banned on aircraft, so why do they still have ashtrays? Despite the rules, ashtrays in bathrooms are a legal requirement by the Federal Aviation Administration (FAA), according to Time. This is because, despite of all the warnings, people might still try and get away with a crafty smoke in the loos, and if they do, there needs to be somewhere safe to stub out their cigarette - a lavatory’s waste bin contains flammable material, so you can rule that out.

The regulation is taken so seriously that a Mexico-bound British Airways flight was grounded in 2009 after it was discovered not to have any ashtrays on board.

22 12. We Never Knew: A Secret Bedroom On Board

When they're not at the beck and call of demanding passengers, have you ever wondered where the crew go to catch a break?

Most long-haul aircraft are designed with crew compartments, which is a little somewhere for attendants to grab a nap and have a breather. Pilots, however, go one better and have a secret bedroom.

Typically located behind the cockpit and above first class, these small rest cabins usually contain a bed, reclining seats and, if they’re lucky, a bathroom and TV, according to The Independent.

21 19. Hidden in plain sight: The Escape Plan Marking System On The Floor

In the unlikely event of a fire, things inside the cabin can get pretty smokey and fast. After several onboard fires resulted in huge amounts of thick smoke, aircraft started installing a FPEEPMS, or Floor Proximity Emergency Escape Path Marking System, to you and us.

These markings, which are on the floor or at near-floor level, use photoluminescent elements, which can be seen in poor visibility. This makes it possible for passengers to read the exit signs while remaining down on their hands and knees to avoid smoke inhalation.

20 9. We Never Knew: There are Handcuffs Hidden On Board

They might be cable-ties or they might be of the heavy duty, stainless steel variety, but you can bet there is some kind of device for passenger restraint on board your plane.

A number of conventions - including the Tokyo Convention (1963) and the Montreal Convention (1971) - outline the rules and regulations concerning discipline on board of an aircraft, according to the BBC. Under these agreements, it’s up to a plane's captain to decide whether a passenger needs to be restrained. Cabin crew is also permitted to request help from passengers to detain an individual, should they need it.

19 22. Hidden in plain sight: That Tiny Hole In The Window

If you’ve ever sat in a window seat, you’ll likely have noticed a tiny hole in the bottom of the window, and yes, it’s supposed to be there. Known as a bleed hole, these tiny features act as a sort of safety valve.

According to Mark Vanhoenacker, a British Airways pilot who reports about aviation, the pressure inside an aircraft during flight is much greater than the pressure outside. Windows are triple-glazed and the outer two cabin windows are designed to contain this difference in pressure, but it’s the outer pane that bears most of this pressure, thanks to the breather hole.

18 11. We Never Knew: A Secret Latch To Open The Lavatory...From The Outside

So here’s the bad news: Your lavatory is never really locked. On the outside door of an airplane loo is a little metal plate saying “lavatory.” It’s not just aesthetic, because flip that plate and you’ll find a secret latch underneath that can be used to lock/unlock doors from the outside.

According to The Express, some airlines use this to lock washrooms during take-off and landing to stop people going in. It’s also a safety mechanism to prevent someone from locking themselves away, giving flight crew emergency access if needed.

17 16. Hidden in plain sight: Check Out Those Yellow Hooks On the Wing

If you’re the lucky passenger in “William Shatner’s Seat” (see the first entry on our list), you’ll have a good view of these bright yellow little features.

In event of a landing on water, these little hooks, which are located about a third of the way to the tip of the wing, may prove to be very useful, according to Reader's Digest. When emergency exits are opened and the inflatable slide is rolled out, a rope is attached to the hooks, which gives passengers something to grasp as they evacuate, should the wings be slippery.

16 2. We Never Knew: A Camera In The Cockpit

Despite some pilots objecting, citing privacy laws, several airlines have rolled out cockpit surveillance, which records everything that goes down on a plane’s flight deck.

Air-safety watchdogs have been advocating the use of cockpit video cameras for several years, despite fierce opposition from pilots, who argue that it will interfere with the decision-making process.

The argument in favour is that the camera footage supplements black-box voice and flight-data recorders - which pilots also opposed when they were first mandated. So far, the FAA has refused to make them compulsory, saying the evidence wasn’t compelling enough to do so.

15 25. Hidden in plain sight: The Little Black Triangle

It’s easy to miss, but next time you board a plane, keep your eyes peeled for a little black triangle stuck above the passenger seat with the clearest view of the wing. This sticker marks the location of what has become known as “William Shatner's Seat,” according to The Telegraph.

Airplane windows are a useful safety feature in themselves, allowing crew to check mid-flight for ice or other potential problems that the wings might have.

The Shatner reference comes from an episode of the 60’s sci-fi show Twilight Zone called Nightmare at 20,000 Feet, in which the actor features. From his airplane seat, his character sees a gremlin on the wing, which is not a problem most flights have to contend with in the real world.

14 4. We Never Knew: Onboard Gas Masks (And They're Not For You)

If there’s a fire onboard, cabin crew are the first line of defence - it’s their job to try putting out the blaze. This is why the plane carries gas masks, and why they are for flight attendants only.

Another reason flight crew are issued with gas masks is because they are portable. Passenger oxygen masks are restrictive, but a gas mask allows crew to move up and down the plane to deal with any potential problems. It’s a practical thing.

13 24. Hidden in plain sight: Can You Spot The Undercover Sky Marshal?

How closely do you watch other passengers during a flight? Could the woman sat next to you be an undercover sky marshal, hiding in plain sight? You better hope you never find out - because if you do, things have just got ugly.

Sky marshals are mysterious agents of the skies, tasked with handling dangerous situations aboard commercial flights. And, if he or she is doing their job properly, you’ll never even know they’re there. A sky marshal will only act in case of a suspected act of terrorism or other serious threat, and though they do carry weapons, they’ll only be used in extreme situations.

12 1. We Never Knew: Fire Extinguishers

Most planes will have two types of fire extinguisher - a handheld device, for manual firefighting, which uses liquified gas, and water-based extinguishers.

According to Boeing, gas extinguishers are spaced throughout the cabin and are easily accessible from the aisle or entryway, whereas the water fire extinguisher is typically located near the lavatory and galley area.

But that’s not all. Amazingly, the engines of planes also have built-in fire extinguishers that can be activated from the cockpit and will stop the fire from spreading.

11 23. Hidden in plain sight: You're Sat On Fire-Proof Seat Cushions

It might not feel like it to sit on, but an enormous amount of thought and testing has gone into those uncomfortable airplane seats - even in economy.

With a little help from Nasa, the Federal Aviation Administration undertook a study to determine which type of seat cushioning materials would be most flame-retardant in the event of an in-cabin fire. Today, aircraft seat are required to pass the FAA’s “Oil Burner Test for Seat Cushions,” and seat protection doesn’t stop there.

All airplane seats must meet tough standards for durability and head-impact protection, and can withstand 16 times the force of gravity.

10 10. We Never Knew: A Secret Seat Button For Extra Space

To be clear, we don’t mean the recline button, oh no. This is a hidden gem that few people know about and, if you’re in an aisle seat, this button will give you a secret advantage.

According to Travel Week, it’s located under the armrest closest to the aisle. Feel under the armrest and you’ll find a button close to the hinge, which allows you to push it upright so it’s flush with the seat.

Without the restriction of the armrest, you’ve got a bit more wiggle room and space to spill into the aisle. This could be a game changer.

9 21. Hidden in plain sight: Those Super Powerful Engines And Precision Engineered Wings

Jet engines are so powerful that a plane can fly just fine if one of them cuts out. What’s even more remarkable is that a plane can also continue to fly even with all its engines down.

Engines provide thrust, one of the four forces of flight, along with lift, drag and weight. And while thrust will push a plane up or forward, it’s the wings that will keep the plane in the air. Engines are only part of the equation.

In 2001, Air Transat Flight 236, carrying 293 passengers and 13 crew, lost power in both its engines over the Atlantic Ocean and managed to glide without any power for a whopping 19 minutes, covering some 75 miles, until landing safely at Lajes Air Base. There were no casualties. This incident has gone down in aviation history as the furthest flown by a passenger jet with no engine power.

8 3. We Never Knew: A Hidden Axe Or Crowbar

There’s a secret weapon inside the cockpit, but it’s there for a very good reason. The Federal Aviation Authority (FAA) mandates that all commercial aircraft must carry an axe in case of an electrical fire, and the cockpit is the safest place to stash it.

Axes are a part of a flight crew’s fire-fighting equipment and can be used to break through panels. You might still see them today - actually, it’s probably a good thing if you don't - but most airlines have replaced axes with crowbars as an anti-threat measure.

7 20. Hidden in plain sight: Yes, That Is A Handrail Moulded Into The Fuselage

You may have noticed it yourself, or you may have seen flight crew make use of it during a spot of turbulence, but along the skirting of the overhead lockers, there is often a handrail moulded into the fuselage.

So if you need to make your way to the lavatory and things get unexpectedly bumpy, don’t just reach for the nearest passenger chair and risk accidentally clonking a fellow flyer on the head. Look up and reach for the handrail - that’s what it’s there for.

6 7. We Never Knew: A Cocktail Of Chemicals Above Your Head

We know a little yellow face mask pops down if a cabin loses pressure, but where does the oxygen come from? Where, and how, is it stored? It’s probably way more complicated than you think.

Having a pressurised canister of oxygen stored above the head of every passenger seat would not be weight or space efficient. Instead, there’s a cocktail of powders and liquids - usually barium peroxide, sodium chlorate and potassium chlorate – which, when activated, react together to rapidly produce oxygen, according to the Huffington Post. It’s a pretty nifty bit of science.

5 15. Hidden in plain sight: Don't Forget The Humans In Charge

We hear a lot about how much reliance is placed on autopilot and other technology, but although these aspects play a vital role in modern day commercial flight, we shouldn’t underestimate the importance of the pilot and flight crew.

Pilots are highly skilled and require around two years of training, including six to nine months of theoretical training before they’re even allowed onto an aircraft or simulator. Then they need to achieve a set amount of flight hours, and complete ongoing training even after qualification. They're responsible for pre-flight checks and decisions in the sky.

Cabin crew also undergo rigorous training, which includes firefighting and human resuscitation. These guys know what they’re doing, and they take the responsibility of passenger safety extremely seriously.

4 5. We Never Knew: The Onboard Emergency Defibrillator

It's not mandated medical equipment but more and more airlines are equipping their aircraft with defibrillators, regardless of whether they’re on long or short-haul routes.

Survival from cardiac arrest doubles when a bystander steps in to apply an automated external defibrillator (AED) before medical responders arrive, according to research in the American Heart Association's journal Circulation. Qantas was one of the first airlines to introduce AEDs on all its aircraft and Emirates, British Airways, Lufthansa, EasyJet and Virgin Atlantic have since followed suit.

In 2015, a coroner called for all commercial aircraft to carry defibrillators after a 47-year-old British woman suffered a cardiac arrest and died on a Ryanair flight. Soon after, the airline announced its entire fleet of aircraft would now carry them.