A look at aircraft windows and what happens if an aircraft window breaks

What Happens If an Airplane Window Breaks? Dramatic Scenarios Explained.

If you’ve ever wondered what would happen if an airplane window broke — dramatic movie-style suction or slight increase in noise — you’re in the right place!

In this blog post, we’ll continue on our journey through the realities behind dramatic situations and look at what happens when things go spectacularly wrong. Can, you even break an airplane window? 

While exceptionally rare. It turns out you can — ask the British Airways pilot who survived being sucked out mid-flight!

We’ll take an informed look at the consequences of a broken window on a plane in mid-flight:

  • Just how difficult is it to break an airplane window?
  • What are the immediate physical effects for anyone in the cabin?
  • What are the flight attendants trained to do?
  • Do the pilots have a checklist or set procedure for broken windows?

So, from pressurisation drops and fog in the cabin, to oxygen masks and potentially being sucked outside, here’s an overview of what happens if a window breaks mid-flight.

I think I can see a crack / the window has fallen out onto the seat!

Let’s start this article with some reassurance. Incidents are high-profile for a reason, airplane windows breaking are exceptionally rare.

What is far more common is the interior layer of Perspex — designed to provide a layer of insulation and keep passengers away from the cold, toughened glass — can come loose or get scratched.

Both our experts, Captain Josh and FA Alissa, have had previous flights where this has occurred.

What if the window looks cracked or scratched? It’s almost certainly the initial layer that is scratched. In fact, this layer is actually called a scratch pane, and is designed for precisely that reason.

Double layered aircraft cabin window

So, if the thin layer of plastic covering the window falls out, don’t panic! Do let the onboard team know, as it will need to be fixed by engineering, but this thin plastic layer has nothing to do with the structural integrity of the window!

How strong are airplane windows?

Cabin windows

The cabin windows on commercial airplanes are made with multiple layers of acrylic glass. The outer pane is about 10 mm thick, while the inner pane is thinner at around 5-10 mm.

Both layers of an aircraft window are structural, so there are two layers of redundancy. What this means is that even if the outermost layer of an airplane window is totally removed, even at the highest cruising altitude — where the pressure differential is the highest — the inner pane can take the stress.

Flight deck windows

The forward facing windows in the flight deck are even stronger than their counterparts in the cabin. Cockpit windows are triple layered, with each layer strong enough to withstand the maximum force on their own.

Boeing 777 with shattered pilot windscreen

There are three key reasons for this.

  1. The forward facing windows are bigger, and are subjected to more stress
  2. The obvious one — they are required by the pilots and are crucial to landing the plane safely!
  3. As part of initial design testing, cockpit windows have to be able to withstand impact from birds

Heated windows — Did you know?

Cockpit windows achieve an additional level of strength by heating! At cruising altitudes, aircraft experience temperatures as cold as -70 degrees Celsius. At this temperature, materials become brittle and easier to shatter.

Alpine views from a cabin window

Cockpit windows are subjected to intense testing — that includes firing frozen chickens out of a high-pressure cannon! — and need to maintain flexibility and strength. They achieve this through inbuilt heating elements, keeping the windows at a higher temperature than the outside air.

What happens if an airplane window breaks?

It is reassuring to know that virtually all aircraft windows are reinforced and duplicated, so the first answer is — absolutely nothing will happen! However, if all the layers of polycarbonate totally fail, the results can be quite dramatic.

There are a few things that can happen:

  • Initially, it will get very noisy. Aircraft cruise at over 500 mph (ca. 805 km/h), and the wind noise will be very loud.
  • At the same time, the cabin will rapidly lose air pressure. The rate of change will depend on the aircraft current altitude, the higher the altitude, the faster the drop in pressure.
  • At cruising altitudes, it will get freezing and foggy in the cabin. The aircraft cabin air is considerably hotter and more humid than the freezing outside air. As the air pressure and temperature drops, the water vapour in the air will become visible.
  • If the aircraft is above 12-15,000 ft passenger oxygen masks will automatically drop from the ceiling, to provide passengers with breathable air

There is no escaping it, as a passenger, the experience is likely to be a very uncomfortable assault on the senses. A rapid loss in pressurisation will likely cause short-term pain in sinuses, tremendous noise, cold and potentially fog, obscuring vision.

However, while uncomfortable, it is still a safe situation. Passengers should remember to always attach their oxygen masks whenever they drop, and follow the instructions of the crew.

What will the flight attendants do?

Like all emergencies, flight attendants are well-trained and will have a series of airline specific procedures that they will perform if a window breaks.

These typically involve:

  • Ensuring they are protected from higher cabin altitudes by using the nearest dropdown oxygen mask.
  • Checking the automatic emergency announcements are correctly informing passengers, or manually announcing these announcements.
  • Checking in on the pilots to ensure that they are OK, and that the pilot oxygen masks are working correctly.
  • Informing the pilots of any damage in the cabin, and getting an update on how long the masks will be required to be worn for.
  • Switching to portable oxygen devices to begin moving around the cabin and helping passengers unable to attach their oxygen masks

Window fail checklist: What do pilots do when a window breaks?

Pilots are trained to deal with numerous emergencies, including window failures.

Here’s a copy of a real checklist — from an Airbus aircraft — displaying what they would do if they had a cockpit window failure in flight:

Airbus pilot broken window checklist procedures

Checklist walkthrough

  • Ensure the pilots are safe (strap in to avoid getting sucked out!)
  • Check the window for damage, if no damage to the inner layer, continue as normal

If the window damage has made it through to the inner layer:

  • Protect themselves by putting on their oxygen masks descend the aircraft to a lower altitude
  • Raise the cabin altitude
  • Both these actions are to ensure that the pressure differential on the window (between outside air and the cabin, is reduced to the minimum)
  • If the windscreen damage obscures their visibility, consider performing an automatic landing if the airport and aircraft are capable.

Summary

In the event of a window failure, it is important to remain calm and follow the onboard crew’s instructions. Events are exceptionally rare, and because aircraft windows have two or even three layers of redundancy, the majority of broken windows on board aircraft will not be structural. Total window failures are almost unheard of.

However, in the extremely unlikely event that an aircraft window totally breaks, hopefully this article has provided reassurance. It is critical to keep in mind that while the cabin may lose air pressure, and it may get cold, the airplane will not fall out of the sky or break into pieces!

By following the normal instructions, such as keeping your seatbelt fastened, and placing your mask on before others — as advised on the initial Captain’s PA — passengers will remain protected.

The bottom line
Whilst an unpleasant situation, the oxygen masks are there to provide you with the oxygen you need in the event of a sudden loss of cabin pressure. Pilots and flight attendants are well-trained to deal with this emergency, and will descend the aircraft to perform an emergency landing.

Share this article
Josh
Josh

Flyingbynumber’s Resident Airline Captain — Josh

Articles: 34