One of the most important developments in the long-term improvements in aviation
safety was the jet engine. Between 1946 and 1958, the United States averaged
three major plane accidents and 42 fatalities a year in accidents caused
primarily by engine failures. Since the introduction of the passenger jet in the
late 1950s, the number of crashes due to engine failure plummeted, as did the
total number of plane accidents.
While traditional piston engines improved greatly through the 1930s and '40s, they did not offer satisfactory reliability.
While traditional piston engines improved greatly through the 1930s and '40s,
they did not offer satisfactory reliability. In fact, as power increased (an
objective in developing military planes), reliable endurance tended to
decrease. By the 1950s, the best piston engines available could only run 1,500
to 2,000 hours before they required overhauls.
All this changed with the jet engine. In 1958, National Airlines launched its
jet service between New York and Miami. These early jet engines extended the "time
between overhaul" (TBO) to 6,200 hours and then to 20,000 hours. Today, with proper
maintenance, jet engines can perform up to 50,000 hours before a complete overhaul is needed.
The Boeing 707, the first commercially successful jet engine-powered plane, marked a new era of safer, more powerful airplanes.
The increased performance level of jet engines affects safety in a number of
ways. Most obviously, the reliability of jet engines ensures that crashes due
to engine failure are uncommon events. Jet engines also allow planes to fly
longer and faster, enabling planes to travel to a different airport if their
original destination proves unsafe for landing. Finally, powerful jet engines
allow planes to fly above dangerous storms and turbulence. back to top
The Flight Data Recorder is a powerful tool for avoiding plane accidents. This
instrument provides investigators with information necessary to determine the
cause of an accident. It also educates aircraft engineers striving to build
planes whose improved design ensures that similar accidents will not happen.
Early flight recorders recorded time, air speed, altitude, vertical acceleration, and heading on metallic foil.
In 1957, the U.S. Civil Aeronautics Board adopted a rule requiring an approved
Flight Data Recorder (FDR) aboard air carriers and commercial airplanes over
12,500 pounds. These early FDRs recorded time, air speed, altitude, vertical
acceleration, and heading. Styluses inscribed this informaion graphically on a
moving roll of metallic foil.
Today's flight recorders can keep track of more than 700 parameters, which are stored on computer chips.
Later, magnetic tape replaced foil recorded more detailed information. With improved technology, more detailed information
was provided by FDRs. Today, the most advanced recorders use digital
solid-state devices that store flight information on computer chips. These more
reliable and crash-worthy FDRs are capable of keeping track of more than 700
parameters, including pitch, roll, and control column position.
How does one go about finding the FDR, or "black box," after an accident? For
one thing, the FDR is not black at all, but rather bright orange, and it's
covered in reflective material, making it easier to locate. In addition, a
sonar pinger is attached to each recorder. These pingers have their own
batteries and are activated by water. Once initiated, the box will emit a sound
every second for 30 days.
In order to ensure that the FDR survives the crash, it undergoes a series of
tests. Shot from a pneumatic cannon at a solid barrier, the storage media must
be able to withstand an impact of 3,400 G's. (G's measure the force exerted by
gravity on a body as it is accelerating.) Penetration resistance is tested by
pounding a quarter-inch-diameter hardened steel rod with a force of 500 pounds
at the recorder's weakest point. Flames of 2,000°F engulf the FDR, which
also must be capable of surviving for 30 days under 20,000 feet of saltwater. back to top
Flying in clouds or in darkness poses some major risks, the most basic of which is
inadvertently flying into the ground. While the plane may be in complete
control, loss of visibility may result in a severe accident with mountainous
terrain or flat ground other than the intended landing site. These crashes,
called "controlled flight into terrain" (CFIT), were major problems until one
piece of technology presented an extremely effective solution.
Early Ground Proximity Warning System displays offered basic but vital information, which enabled pilots to avoid controlled flight in terrain, once a devastating problem in commercial flight.
Ground Proximity Warning System (GPWS) monitors the aircraft's height above
ground as determined by a radio altimeter. A computer then keeps track of these
readings, calculates trends, and can predict trouble ahead. An audible warning
is given if there is any possibility of danger. If the plane is descending at
too steep an angle during descent, is descending too rapidly, has insufficient
terrain clearance, or is flying towards higher terrain, the pilot is given a
warning to make adjustments immediately. Since the U.S. Federal Aviation
Administration (FAA) required large airplanes to carry such equipment in 1974,
the number of accidents due to CFIT has dropped from 7-18 a year to 1-2 a
Today's Enhanced Ground Proximity Warning Systems can accurately predict potential dangers using the Global Positioning System. These detailed displays indicate the contours of approaching terrain and designate their proximity to the airplane's altitude with colors.
Traditional GPWS does have a blind spot. Since it can only gather data from
directly below the aircraft, it must predict future terrain features. If there
is a dramatic change in terrain, such as a steep slope, the GPWS will recognize
the trend only very near the dangerous terrain. A new piece of technology, the
Enhanced Ground Proximity Warning System solves this problem by combining a
worldwide digital terrain database with a Global Positioning System. With these
tools, the plane can pinpoint its position and compare it with a stored map of
all of the contours of the Earth's surface. The pilot can easily observe the
contours of the surrounding terrain, and a warning system can give an early
warning signal when any features ahead may pose a collision threat. back to top
As airplanes began to fill the sky, mid-air collisions became a real threat.
In 1976, public concern over these accidents lead to the Separation Assurance
Program, which, among other things, called for the development of the Beacon
Collision Avoidance System (BCAS). The search for such a device was not new.
As early as 1955, the Air Transport Association had been working to develop
this equipment; the FAA joined the search in 1959. By 1976, the FAA had
implemented a conflict alert system, capable of warning air traffic controllers
of less-than-standard separation at all 20 air-route traffic control centers in the U.S.
The FAA tests the Boeing 727 and its Traffic Alert and Collision Avoidance System (TCAS) equipment.
In 1981, an important improvement was made to the BCAS system, which was unable to
function in areas of extreme air traffic. The FAA adopted Traffic Alert and
Collision Avoidance Systems I and II (TCAS I and II). Combining radio
transmitters and receivers, directional antennas, and computer and cockpit
displays, these TCASs transmit a radio signal called an interrogation. Other
airplanes in the area receive these signals and transmit replies. Finally,
computers calculate the distance between the planes based on time between
the interrogation and the reply.
This Traffic Alert and Collision Avoidance System II Display indicates traffic dead ahead 600 feet below and another aircraft coming at 400 feet above. The pilot will get an advisory to climb or descend if the TCAS computer calculates that a collision hazard exists.
TCAS I systems provide pilots with the altitude and the "o'clock" position of nearby planes. The high end TCAS II system provides more sophisticated advisories, including data on the range and bearing of nearby planes. These
systems can even suggest escape maneuvers. In 1989, the FAA required TCAS
II on all airlines with over 30 passenger seats operating in U.S. airspace.
Planes with 10 to 30 seats were required to install TCAS I. back to top
A microburst descends from a storm and sends strong surface winds outwards, creating a dangerous situation for planes that are landing or taking off.
Wind shear poses one of the most dangerous threats to low-flying airplanes.
Downward "microbursts" of wind originate from thunderstorm activity and fall to the
Earth. Upon contact with the ground, this dense burst of air radiates outwards,
generating dangerously strong surface winds. Approaching wind shear conditions,
the pilot would experience headwinds followed by equally strong tailwinds. The
combination of these two forces can dramatically reduce air speed (the airplane's
speed relative to the surrounding air) and rob the wings of their lift, resulting
in a crash.
The first approach to combating this problem was a Low Level Wind Shear Alert
System (LLWAS) that became operational at major airports in 1978. This system
detected severe downdrafts and wind changes with wind speed and direction sensors
around the airport periphery. When a microburst was detected, an alarm sounded in
the control tower, and pilots in the area were informed.
By 1988, the FAA issued a rule that went a step further: All turbine-powered airliners
seating 30 passengers or more must carry equipment that both warns pilots when
they encounter low-altitude wind shear and provides them with information to
escape safely. At first, these systems were reactive: Detecting sudden changes
in airspeed due to horizontal wind, an alarm informed the pilot that they were
flying in wind shear conditions. The pilot was then able to react properly and
New, forward-looking wind shear detectors make visually clear to pilots hazardous wind shear conditions ahead.
New forward-looking detectors use radar to predict upcoming weather events, including
wind shear. The system bounces energy pulses off the rain droplets or moisture of
the upcoming region and analyzes the distance to a potential problem area by measuring
the time it takes the pulse to return to the aircraft. This radar can even detect
which way the air is moving by analyzing the way that the pulse was reflected back:
If it bounces off downward-moving particles, a higher frequency is returned than if
it bounces off particles moving horizontally. These new forward-looking wind shear
detectors can give pilots as much as 90 seconds warning before entering a wind shear
system, giving them time to make the necessary adjustments. back to top
Satellites positioned around the world have enabled pilots to use the Global Positioning System to accurately determine their coordinates.
Aircraft safety only continues to increase with the new technologies that have recently
been developed. In 1983, the first aircraft to navigate across the Atlantic
entirely by use of the Global Positioning System (GPS) landed safely in Paris.
Using satellites in space, pilots can pinpoint their position on the globe with
More recently, new navigational systems have built upon the success of GPS. In
1996, the Driver's Enhanced Vision System became operational at Boston Logan
airport. This equipment, which uses satellite, digital, and infrared
technologies, assists emergency crews when visibility is limited by smoke,
flames, fog, or precipitation.
The Local Area Augmentation System (LAAS) may enhance the accuracy of the Global Positioning System enough to allow pilots to use GPS to make precision landings with zero visibility.
Even more cutting-edge technology is becoming available. Today, pilots can make
precision landings with zero visibility using radio signals to guide them to
the runway. Developers are currently testing equipment to use GPS to land
planes. In order to do this, pilots need to know their location with even more
precision than GPS can offer. To provide this accuracy, stations around the
airport receive information from GPS satellites, compare these data with their
own exact location (which they can determine with extreme accuracy), and send a
signal that will correct their GPS data. This system, called the Local Area
Augmentation System, is currently under development and may eventually provide
accurate, less-expensive ways for airports to bring in their planes.
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Photos/Illustrations: (1,3,5,7-9) National Archives/FAA;
(2) Courtesy of Boeing;