What Everyone Gets Wrong About Planes

Plane doors remain unlocked because the immense pressure difference between the pressurized cabin and the outside at high altitudes makes them impossible to open mid-flight. This pressure is essential because the air at cruising altitudes of 30,000-40,000 feet is too thin to breathe. Planes fly high primarily for efficiency: thinner air means less drag, allowing planes to fly faster and burn less fuel, saving airlines money.

The cabin is pressurized to about 77 kilopascals, creating an oxygen partial pressure of 16 kilopascals, the minimum for human survival. This pressurization requires plug-shaped doors that seal tightly inward. This system is crucial, as a catastrophic failure like the Aloha Airlines incident in 1988 demonstrated, where a crack in the fuselage led to the roof tearing off. Planes are pressurized to the least extent possible to minimize stress on the fuselage and extend their lifespan, a trade-off that ensures safety while prolonging aircraft viability.

The rule about putting phones on airplane mode is largely a relic of past concerns about interference with navigation systems, though a phone has never been proven to cause an air accident. The EU is moving away from this requirement, and the taste of airplane food is affected by dry cabin air and lower pressure, which dulls the senses of smell and taste, though certain flavors like tomato juice are surprisingly enhanced due to cabin noise stimulating umami receptors.

• Plane doors are not locked because the high cabin pressure at cruising altitudes makes them impossible to open from the inside.
• Planes fly at 30,000-40,000 feet for fuel efficiency, as thinner air reduces drag, allowing for faster speeds and less fuel consumption.
• Cabin pressurization to approximately 77 kilopascals is necessary because the outside air at high altitudes is unbreathable due to low pressure.
• The taste of airplane food is altered by dry cabin air and lower pressure, which affect smell and taste perception, while cabin noise can enhance the flavor of tomato juice.
• The requirement for airplane mode on phones is largely outdated, stemming from historical concerns about interference that have not been substantiated by evidence of accidents.

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Why Plane Doors Aren't Locked [0:08]

• Most plane doors are not locked, lacking keys, sensors, or passcodes.
• The primary reason they aren't opened in flight, despite 40 million flights annually, is not security but physics.
• Passengers generally exhibit self-preservation and common sense, not attempting to open them.

The real reason plane doors are virtually never opened mid-flight lies in the physics of flight. While seemingly unsecured, the immense pressure difference between the cabin and the outside at high altitudes creates an unassailable seal.

The Science of Altitude: Why Planes Fly High [1:24]

• Planes fly at altitudes of 30,000 to 40,000 feet (approximately 10 km).
• Flying high offers a smoother ride by avoiding most weather in the troposphere, reducing turbulence.
• The main reason is economic: air density decreases significantly with altitude. At 33,000 ft (10 km), air density is one-third of sea level.
• This lower density means less drag, allowing planes to fly about 73% faster for the same thrust.
• Consequently, planes reach destinations faster, burn less fuel, and save money.
• Climbing uses more fuel (80 kilos/minute) than cruising (40 kilos/minute), with descent using minimal fuel (around 10 kilos/minute).
• Jet engines are more efficient at higher altitudes because the colder air (around -50°C) improves combustion.
• Flying high also allows planes to utilize jet stream tailwinds, further increasing efficiency and reducing costs.

The bigger reason, of course, is money.

The decision to fly at high altitudes is a strategic one, driven by significant economic benefits. Reduced air density translates to faster travel times and substantial fuel savings, making flights more profitable for airlines. This efficiency is further enhanced by the improved performance of jet engines in the cold, thin air and the utilization of favorable jet stream winds.

The Necessity of Cabin Pressurization [4:00]

• At high altitudes, the air is unbreathable due to low air pressure.
• At 10 km, air pressure is only a quarter of sea level pressure.
• While oxygen content remains 21%, the partial pressure of oxygen drops, preventing enough oxygen from entering the bloodstream.
• Humans need an oxygen partial pressure of at least 16 kilopascals to function normally.
• Airplane cabins must be pressurized to maintain breathable air.
• Pressurization uses a small amount of air from the jet engine's compression stage.

The downside is that you are taking away a little bit of the efficiency of the engines.

The thin air at cruising altitudes necessitates cabin pressurization to ensure passenger safety and comfort. This process involves supplying compressed air to the cabin, a critical system that, while effective, does slightly reduce engine efficiency.

The "Plug Door" Design and Its Implications [5:03]

• Before pressurization, planes flew around 10,000 feet where oxygen levels were manageable, and doors opened outward without much concern for seals.
• With pressurization, doors were redesigned to be "plug" doors, wider on the inside than the outside.
• This design ensures the higher cabin pressure pushes the door into its frame, creating an airtight seal.
• The pressure difference is so significant that even modern doors, which are ingeniously designed to open inward before rotating outward, cannot be opened by force mid-flight.
• Forcing a plug door inward at altitude would require a force equivalent to lifting 9,000 kilograms.
• Cabin pressure is not fully sea-level pressure (101.3 kilopascals); it's typically around 77 kilopascals at cruising altitude.
• This lower cabin pressure causes items like chip bags to inflate.
• It also leads to increased gas expansion in the body, contributing to more flatulence on planes.

It's that movement inwards that is impossible at altitude.

The "plug door" design is a marvel of engineering, ensuring cabin integrity through a simple yet powerful application of physics. The inward-facing design, combined with the substantial pressure differential, makes accidental or intentional opening of emergency exits virtually impossible during flight.

Minimizing Stress: The Reason for Partial Pressurization [7:55]

• The International Space Station is pressurized to sea level pressure (101.3 kilopascals).
• Planes are pressurized to the minimum extent necessary for passenger comfort and survival (around 77 kilopascals).
• This is to minimize stress on the aircraft's fuselage.
• Planes experience repeated cycles of stretching (during pressurization) and relaxing (during depressurization) with each flight.
• The Aloha Airlines Flight 243 incident in 1988, where a crack caused the roof to tear off, highlighted the dangers of fuselage fatigue.
• That plane had nearly 90,000 flight cycles, exceeding its design limits, leading to fatigue, cracking, and explosive decompression.
• Pressurizing to the least extent possible reduces these stresses, prolonging the lifespan of the aircraft.

So, planes are pressurized to the least extent possible to minimize stresses and extend the life of the plane.

The decision to maintain a lower cabin pressure than sea level is a critical safety and longevity measure. By minimizing the pressure differential, airlines reduce the cyclical stress on the aircraft's structure, preventing fatigue and extending the operational life of the plane, thereby mitigating risks like those seen in the Aloha Airlines incident.

The "Airplane Mode" Debate: Interference and Rules [9:30]

• A passenger once managed to open an emergency exit in flight on final approach, where the pressure differential was minimal.
• This event was considered unusual and required extreme force.
• The rule about putting phones on "airplane mode" is a common instruction, but its necessity is often questioned.
• Historically, the FAA banned personal electronics in 1961 due to concerns from portable FM radios interfering with navigation systems.
• Airlines could override the FAA ban, but phones remained restricted due to FCC jurisdiction.
• The FCC's concern was that phones in the air could overload ground cell tower infrastructure by connecting to multiple towers simultaneously.
• However, a plane acts as a Faraday cage, blocking most signals. Phone signals would have to escape through windows and travel long distances horizontally.
• Cell towers are tilted downwards, making it difficult for airborne phones to connect unless flying very low.
• The FCC never tested this specific concern, and the ruling has persisted.
• All airplane mode definitively does is save battery life.
• Some anecdotal reports link specific interference sounds in cockpit communications to active phones, though the impact of a single phone is likely minimal.
• The EU no longer requires airplane mode and is pushing for airlines to offer 5G service.

As far as we know, a mobile phone has never caused an air accident.

The "airplane mode" rule is a legacy regulation rooted in past technological concerns that have largely been invalidated by modern understanding of electronics and aircraft shielding. While it conserves battery life, its impact on flight safety is negligible, and international regulations are beginning to reflect this.

The Curious Case of Airplane Food Tastes [11:40]

• Airplane food is often perceived as bland or unappetizing.
• Several factors contribute to this:
  • The dry cabin air (as low as 5% humidity, compared to the Sahara's 25%) dries out nasal passages, hindering smell and thus taste.
  • Lower cabin pressure can decrease the sensation of saltiness and sweetness.
• However, certain flavors are enhanced at altitude.
• Tomato juice is a popular drink on planes, with over a quarter of surveyed flyers ordering it, and 23% would not drink it on the ground.
• This preference might be due to cabin noise stimulating the chorda tympani nerve, which carries taste information and runs near the eardrum.
• Loud noise can create an audio illusion that boosts the sense of umami, the savory taste found in tomatoes.

So, next time you're on a flight, go for something extra sweet or salty or maybe try the tomato juice.

The peculiar taste of airplane food is a complex interplay of environmental factors within the cabin. Dry air and lower pressure dampen taste perception, but surprisingly, the ambient noise can amplify certain flavors, making drinks like tomato juice a surprisingly popular choice at 30,000 feet.

Learning from Accidents: The Safety of Aviation [13:30]

• Aviation safety is a result of deeply analyzing accidents and incidents.
• Professionals meticulously investigate these events to learn from them, making each subsequent flight safer.
• Understanding these investigations can paradoxically make people feel safer about flying.
• Media often prioritizes sensational headlines over nuanced details, contributing to public perception.
• Ground News is highlighted as a tool to see the whole picture and verify information sources by comparing media coverage.
• The discussion touches on how climate change might increase turbulence, noting that media coverage can be skewed.
• Ground News helps identify "blind spot" stories that the media might overlook.

The fact that we have hundreds of professionals that dig deep into these accidents means that we learn from them. So, every flight becomes a little bit safer.

The exceptionally high safety record in aviation is not a matter of luck but a testament to a rigorous culture of learning from every incident. By dissecting accidents and sharing those lessons, the industry continually refines its practices, making flying one of the safest modes of transportation.