The strength and security of the pilots door on commercial airliners has become a critical issue in aviation safety since the terrorist attacks on September 11, 2001. Prior to 9/11, pilots doors were often flimsy and unable to withstand determined intruders. However, since that fateful day, regulators and airlines have worked hard to reinforce and secure the pilots door against unauthorized access. But just how strong are these fortified doors and what are they made of? Let’s take a closer look at the requirements, materials, tests and technology behind today’s hardened cockpit doors.
Why are reinforced doors needed?
Prior to 9/11, pilots doors were often little more than a privacy divider, unable to keep out intruders intent on entering the cockpit. This vulnerability allowed the 9/11 hijackers to overpower the pilots and take control of the aircraft to disastrous effect. As part of the 9/11 Commission recommendations, requirements were introduced mandating reinforced flight deck doors that could withstand firearms and intrusion attempts. Hardened doors act as a deterrent and the last line of defense, helping to ensure unauthorized access to the cockpit is impossible. Reinforced doors buy precious time for pilots to alert authorities and land safely in the event of an incident. They are now mandated on all airliners in the US and most of the world.
Regulatory requirements
All newly manufactured airliners in the US must have flight deck doors certified to meet strict standards mandated by the FAA. They must withstand sustained attacks with a sledgehammer or ax. Firearms protection up to standard large handguns (.44 Magnum) is also required. The doors must remain operable after sustaining any impacts and attempts at intrusion. There are no set specifications on materials, allowing innovation by manufacturers on how best to meet the requirements. Similar standards are adopted globally by agencies like EASA in Europe and Transport Canada.
Materials used
While the exact construction varies between plane models and manufacturers, most reinforced cockpit doors use a layered design with tough composite materials like Kevlar, carbon fiber and aircraft-grade aluminum. Kevlar has an extremely high tensile strength for its weight and can resist bullets. Carbon fiber is similarly very rigid and resilient to impacts. Outer aircraft aluminum skin further strengthens the door. Internal steel or composite grids are often used to provide an inner baffle that reinforces the door panel. Additional armor plating is also sometimes added for increased bullet protection. Hinges and locks are strengthened to complement the reinforced door materials against attack.
Design innovations
Manufacturers employ innovative designs and features to meet regulatory requirements:
– Extra interior locking pins that insert into the door frame upon closing, creating a hardened barrier.
– Electric solenoid locks that can only be operated from the cockpit to prevent unauthorized opening.
– Impact-resistant window inserts like acrylic glass that allow crew to view outside but prevent bullets penetrating.
– Kevlar blanket lining that stops bullets penetrating the door surface.
– Pressure equalization systems to allow doors to be opened even with significant exterior pressure differential.
– Dual-design doors with an outer door for bullet protection and inner door as main pressure seal.
Testing and approval process
Extensive testing and analysis goes into certifying reinforced doors:
– Computer models simulate forces exerted on doors from impacts, bullets and sledgehammer blows.
– Static tests use hydraulic rams to bend and apply huge pressures to sections of doors to ensure they do not fail.
– Dynamic swing tests involve pneumatic rams violently swinging doors for thousands of cycles to evaluate durability.
– Live fire tests use real firearms shot at doors from multiple angles to confirm bullet resistance.
– Actual doors go through sustained onslaughts from axes and sledgehammers wielded by humans to simulate attacks.
– Pressure tests confirm doors can operate and function properly in pressurized environments.
– Only after successfully passing this barrage of testing are doors certified by regulators as compliant for airline use.
Real world incidents
While fortunately still very rare, real world incidents highlight the effectiveness of reinforced flight deck doors:
– In 2003, a disturbed passenger on a Qantas 717 attacked the cockpit door inflight with metal pipes. Despite sustained hammering, the door remained secure.
– In 2012, passengers restrained an aggressive man trying to break down the cockpit door on an Alitalia flight. The door held firm despite blows from his body.
– A number of additional cases involve agitated passengers kicking and striking cockpit doors but failing to gain entry due to their resilient construction.
Factors still limiting door strength
While reinforced doors are clearly an enormous improvement over past flimsy doors, there are still factors that limit their strength:
– Materials like Kevlar lose some of their strength and impact resistance at the cold temperatures found at cruising altitudes.
– Pressurization needs means doors cannot be as thick and heavy as desired without becoming too cumbersome to operate.
– Bullets fired from high power sniper rifles may potentially still penetrate.
– Hydraulic rams have proven able in tests to bend and crack doors with sustained pressure.
– Hinges and pressure seals remain relatively vulnerable.
Are doors strong enough to stop a missile or grenade?
It’s unlikely reinforced cockpit doors could withstand a direct hit from a missile or grenade. While kept secret, their exact blast resistance isn’t thought to be that extensive. They are designed to stop individual hand-carried weapons like guns and axes, not high explosives. A grenade detonated right against the door would likely cause catastrophic structural failure. Shoulder-fired missiles would also easily blast through the door defenses. Such weapons are also banned from being brought onboard aircraft.
Comparison of door strength by airliner model
| Airliner Model | Door Construction | Certified Strength |
|---|---|---|
| Boeing 737 MAX | Kevlar composite with steel inner frame | Withstands sustained ax and sledgehammer attack. .44 Magnum bullet protection. |
| Airbus A320 | Composite panel with Kevlar and carbon fiber | .44 Magnum bullet protection. Protected against axes and crowbar attacks in testing. |
| Boeing 777 | Kevlar and aircraft aluminum honeycomb | Triple-reinforced. Stopped 7.62mm ball ammunition during certification. |
| Boeing 747-8 | Kevlar composite and aluminum skin | Stopped .44 Magnum and 9mm rounds during live fire testing. |
Are there any weaknesses or vulnerabilities in the doors?
While extremely robust, experts have identified some theoretical weaknesses:
– The locks, hinges and pressure seals are less strong than the door panels themselves. These could be targeted to breach the door’s integrity.
– Sufficient explosives smuggled on board could potentially blast through the door, though bombs are screened for in airport security.
– There are concerns that observation windows in some doors may be vulnerable to high power sniper rounds at close range.
– Doors could potentially be opened in the maintenance hangar by accessing internal actuators. More controls on ground access would be sensible.
Overall however, these concerns are minor compared to the proven capabilities of reinforced doors in keeping cockpits secure. No design can ever be 100% foolproof against every conceivable situation.
Are there new door technologies on the horizon?
Manufacturers and regulators continue researching ways to improve protections even further:
– Triple latch systems that spread loads across multiple locking points.
– Explosive cord around door edges that detonates upon attempted intrusion.
– Reinforced windowless doors to eliminate a vulnerability point.
– New composite materials like pressed graphene sheet that are lighter but even stronger.
– Built-in electrical stun defenses to deter proximity to the door.
– Biometric locks keyed to authorized flight crew only.
However many of these concepts have downsides in cost, complexity or being impractical in the real aviation environment.
Conclusion
Reinforced cockpit doors have proven to be very effective protections for airline safety in the years since their mandating. While not completely impregnable, their layered construction from advanced materials allows them to resist determined attacks and buy valuable time for the pilots. Manufacturers undertake rigorous testing to simulate real world conditions and achieve certification. However, minor vulnerabilities potentially still exist in pressure seals, hinges and windows. New door technologies continue to be researched but have yet to supersede the robustness and reliability of the current generation of hardened doors. While hopefully never needed, reinforced doors provide appreciable extra security for passengers and crew against the small minority of those who would seek to threaten commercial air travel.