What Makes Jetliners Safe
Commercial aviation is the safest mode of transportation. That record has been established through the work of everyone involved in aviation - manufacturers, airlines, airport operators, government regulators, and a highly skilled and dedicated work force.
At the core of the aviation transportation system is the jetliner itself. It has been engineered and built to move passengers and cargo quickly, efficiently and, most importantly, safely. And it does this exceedingly well.
Commercial jetliners are designed with redundancy in all major systems and incorporate all that has been learned over many decades of commercial flight.
Modern jetliners are the most reliable, well-equipped vehicles ever designed. Their safety features include:
- A rugged, damage-tolerant structural design.
- Robust systems design.
- Ample redundancy.
- Improved warning systems and situational awareness.
- Increasing navigational precision.
Flight envelope
Test pilots aren't the only people who "push the envelope." Aircraft engineers use the term too when designing airplanes. The "flight envelope" encompasses the operating capabilities of an airplane in normal commercial use. The "design envelope" builds in capacity well beyond what would normally be used in regular operations.
Except for flight-test crews, most pilots will never approach or exceed the edge of the flight envelope. But, if they ever had to, the airplane would still be readily controllable because of the extra built-in design capability.
Every normal takeoff, climb, cruise, descent and landing takes place within the flight envelope. The envelope defines:
- How slow and fast the jet can fly.
- How heavy it can be at takeoff or when it lands.
- How high it is allowed to go.
- How high or low the pilot can pitch its nose.
- How steeply it can be banked.
- How many g's it can pull.
- How much extra fuel it must carry.
Jetliner features that make it safe during different stages of flight
Jetliners are capable of a great deal more than smooth flights and gentle turns. Jetliner features and crew procedures protect us during each of the following stages of flight:
Prior to takeoff
Pilots go through a detailed, structured process to check safety and airworthiness, including thorough systems checks, before an airplane ever leaves the gate.
Taking off
Even if an engine were to fail at the worst possible time - at takeoff when a jetliner is at its heaviest and has just attained flying speed - the airplane can still take off successfully. In the case of twinjets, they are 100 percent overpowered - they can climb out safely even if an engine quits entirely. A jetliner always travels at least 10 percent faster at takeoff than the slowest speed required to become airborne.
If the pilot decides not to take off, jetliners have outstanding braking ability - and regulations ensure that there is enough runway ahead to stop. In addition, commercial jetliners are designed with large rudders that give outstanding control in the event of an engine failure.
Climbing
Engines operate at high takeoff thrust during climb until a safe altitude is reached. The flight crews then reduce the thrust, which lowers community noise, and the aircraft continues climbing to final cruise altitude.
Cruising
The aeronautical design of commercial jetliners makes them very stable. For example, if a gust of wind pushes the airplane's nose up, the aerodynamics help push it back to where it started.
The structure is designed to withstand 150 percent of the greatest load an airplane might encounter. In addition, test airframes are pressurized over and over again, enough for several lifetimes of normal operation, to validate the design.
Jetliners normally cruise at about 35,000 feet at speeds over 500 miles per hour.
Navigating and communicating
Jetliners contain redundant systems for navigating and communicating. For navigation, there are electronic gyro compasses as well as old-fashioned mechanical compasses as backups. Dual flight management computers make the pilots aware of all aspects of the flight path - where the airplane is at all times and where it is going. Global Positioning Systems today enable jetliners to navigate via satellite for extremely safe and efficient travel. For communication, there are several kinds of radios, with backups.
Controlling attitude and direction
Flight controls facilitate communication between pilot and co-pilot. The pilot cannot move the control stick without the co-pilot knowing it because their controls are linked together.
In addition, there are redundant controls from the pilot to the airplane. The sensors on the jetliner that transmit speed, attitude and stability information back to the pilot also are redundant. (Attitude is the airplane's spatial orientation - its variations in yaw, pitch and roll.)
There are also many warning systems on jetliners that alert pilots to changing situations - with voice commands, horns, buzzers, lights and vibrations.
Descending
For many years, the world jetliner fleet has relied on the ground-proximity warning system (GPWS) to help keep pilots from inadvertently hitting the ground at night or in bad weather. Since its introduction, GPWS has reduced the incidence of controlled flight into terrain accidents, a leading cause of jetliner losses.
Today, a newer version of GPWS is being phased in. The terrain avoidance warning system combines precise GPS navigation and digital three-dimensional terrain data to create a better warning device.
Jetliners also have modern systems to help them avoid collisions and wind shear.
Landing
Landing gears on commercial jetliners are true engineering marvels, capable of withstanding extremely hard landings. When you consider the speed at which airplanes take off and land - up to 235 miles per hour, which is about the same as qualifying racers for the Indianapolis 500 - tires on landing gears are also terrific feats of engineering and contribute greatly to landing safely.
Warning Systems
In addition to ground-proximity warning systems, jetliners have systems and procedures to help them avoid collisions and wind shear.
The traffic alert and collision avoidance system (TCAS) is an excellent example of how technology can make aviation safer. Since 1989, when airlines began equipping their airplanes with TCAS, no midair collisions have occurred between airplanes in the United States and few have occurred anywhere else in the world.
TCAS takes advantage of the fact that all commercial aircraft are equipped with radar transponders. When scanned by ground-based air traffic control radar, these units send altitude, heading, speed and other flight information that controllers see on their screens. TCAS interrogates the transponders of nearby aircraft and uses their responses to look for potential collisions. If TCAS detects a potential problem, it issues warnings to the airplanes and provides directions to help the flight crews steer away from the other airplane.
Wind shear is a sudden change in the wind's speed or direction. Wind shear often involves strong side-by-side updrafts and downdrafts and may occur in conjunction with a thunderstorm or other bad weather. It can have potentially disastrous consequences for a jetliner if encountered near the ground. Appearing with little or no warning, low-level wind shear can overwhelm an airplane's ability to safely descend or climb. Wind shear was the seventh most common cause of fatal jet accidents worldwide during the past 10 years.
The aviation industry has had great success dealing with wind shear. The rate of wind shear accidents has dropped dramatically in recent decades because of
- Specialized training and procedures -- flight crews today know how to fly safely out of wind shear, and they practice these skills in simulators.
- Reactive alerting -- this onboard function warns flight crews when a jetliner is entering possible wind shear conditions.
- Predictive alerting -- this new system looks ahead with special radar to warn of possible wind shear before it's encountered, so pilots can steer around it.
- Ground-based Doppler radar -- more and more airports are getting this special radar, which detects some forms of wind shear.