AIRCRAFT INSTRUMENTS

Distance Distance Measuring Measuring

Equipment (DME)Equipment (DME)

Distance Measuring Equipment Distance Measuring Equipment (DME)(DME)

distance by timing the distance by timing the propagation delay of propagation delay of VHF or or UHF radio radio signals by sending and signals by sending and receiving pulse pairs – receiving pulse pairs – two pulses of fixed two pulses of fixed duration and separationduration and separation

invented by invented by Edward George "Taffy" Bowen

ground stations are ground stations are typically collocated typically collocated with with VORs

DME system is DME system is composed of a UHF composed of a UHF transmitter/receiver transmitter/receiver (interrogator) in the (interrogator) in the aircraft and a UHF aircraft and a UHF receiver/transmitter (receiver/transmitter (transponder) on the ) on the ground.ground.

A radio pulse takes around 12.36 microseconds to A radio pulse takes around 12.36 microseconds to travel one nautical mile to and from, this is also travel one nautical mile to and from, this is also referred to as a radar-mile. referred to as a radar-mile.

The time difference between interrogation and The time difference between interrogation and reply minus the 50 microsecond ground reply minus the 50 microsecond ground transponder delay is measured by the transponder delay is measured by the interrogator's timing circuitry and translated into interrogator's timing circuitry and translated into a distance measurement in nautical miles which a distance measurement in nautical miles which is then displayed in the cockpit.is then displayed in the cockpit.

DME interrogator uses DME interrogator uses frequencies from 1025 frequencies from 1025 to 1150 MHzto 1150 MHz

DME transponders DME transponders transmit on a channel transmit on a channel in the 962 to 1150 in the 962 to 1150 MHz range and MHz range and receive on a receive on a corresponding channel corresponding channel between 962 to 1213 between 962 to 1213 MHzMHz

The band is divided into The band is divided into 126 channels for 126 channels for interrogation and 126 interrogation and 126 channels for channels for transponder repliestransponder replies

The interrogation and The interrogation and reply frequencies reply frequencies always differ by 63 MHzalways differ by 63 MHz

DME facilities identify DME facilities identify themselves with a 1350 themselves with a 1350 Hz morse code three Hz morse code three letter identityletter identity

the physical distance the physical distance from the aircraft to the from the aircraft to the DME transponderDME transponder

depends depends trigonometrically upon trigonometrically upon both the altitude both the altitude above the transponder above the transponder and the ground and the ground distance from itdistance from it

TACTICAL AIR NAVIGATION TACTICAL AIR NAVIGATION (TACAN)(TACAN)

Tactical Air Navigation Tactical Air Navigation (TACAN)(TACAN)

provides the user with provides the user with a distance and a distance and bearing from a ground bearing from a ground stationstation

provides the following provides the following pieces of information:pieces of information:– BearingBearing - provides - provides

magnetic bearing to the magnetic bearing to the station you are tuned tostation you are tuned to

– DistanceDistance - slant range - slant range to the station up to 390 to the station up to 390 nautical milesnautical miles

– To/FromTo/From - flying away - flying away or towards your station. or towards your station.

– Beacon Identifier Beacon Identifier Tone (BIT)Tone (BIT) - audio - audio information consists of information consists of a morse code trail for a morse code trail for identification of the identification of the station you are tuned tostation you are tuned to

– ReliabilityReliability - warning - warning flag information lets flag information lets you know if the system you know if the system is reliableis reliable

TACAN station with no aircraft initially modulates TACAN station with no aircraft initially modulates squitter onto the carrier, which is basically squitter onto the carrier, which is basically random noise generated so that the waveform is random noise generated so that the waveform is the proper length. So basically, you end up with a the proper length. So basically, you end up with a signal which is simply noise: signal which is simply noise:

When an aircraft flies into range which is When an aircraft flies into range which is transmittingtransmitting distance interrogations, the station distance interrogations, the station will pick these interrogations up and generate an will pick these interrogations up and generate an appropriate response by pulse modulating DME appropriate response by pulse modulating DME data into the waveform. data into the waveform.

every 30 seconds, the station modulates station every 30 seconds, the station modulates station identification in the form of BIT data onto the identification in the form of BIT data onto the carrier:carrier:

RF energy from the TACAN transmitter RF energy from the TACAN transmitter is fed to the antennais fed to the antenna

Parasitic elements positioned around it Parasitic elements positioned around it are electronically rotated at 15 are electronically rotated at 15 revolutions per minuterevolutions per minute

The distance of the parasitic element The distance of the parasitic element are chosen to obtain a radiation patternare chosen to obtain a radiation patternthat looks like this:    that looks like this:    

as the reflector moves, as the reflector moves, the outward lobe of the the outward lobe of the cardioid-like radiation cardioid-like radiation pattern moves aroundpattern moves around

this creates a physically this creates a physically amplitude modulated amplitude modulated signal, which each signal, which each aircraft sees differently.aircraft sees differently.

Because of the rotating Because of the rotating radiation pattern, the radiation pattern, the waveform is variable for waveform is variable for aircraft at different aircraft at different radials, but all aircraft radials, but all aircraft receive the receive the referencereference signal at the same timesignal at the same time

the aircraft determines its bearing the aircraft determines its bearing from the station by looking at the from the station by looking at the waveform of the signal and where waveform of the signal and where the main reference burst is pulse the main reference burst is pulse encoded.encoded.

To provide more accurate bearing information, To provide more accurate bearing information, TACAN uses the same principle again to calculate TACAN uses the same principle again to calculate fine bearing. Yet another rotating element with fine bearing. Yet another rotating element with 99 reflectors produces even more amplitude reflectors produces even more amplitude variations. Again, there is a reference point for variations. Again, there is a reference point for the variable amplitude variations. This comes in the variable amplitude variations. This comes in the form of the form of 99 auxillary reference bursts: auxillary reference bursts:

And, of course, you still have your main reference And, of course, you still have your main reference burst:burst:

DME responses:DME responses:

And BIT, And BIT, at 30 second intervals:at 30 second intervals:

composite signal (listed below in order of priority): composite signal (listed below in order of priority): 1. MRB - Main Reference Burst1. MRB - Main Reference Burst2. ARB - Auxillary Reference Bursts2. ARB - Auxillary Reference Bursts3. BIT - 1350Hz Beacon Identification Tone3. BIT - 1350Hz Beacon Identification Tone4. DME - Distance Measurement Equipment4. DME - Distance Measurement Equipment5. 2700Hz Squitter/Filler5. 2700Hz Squitter/Filler

TRAFFIC COLLISION TRAFFIC COLLISION AVOIDANCE SYSTEM AVOIDANCE SYSTEM

(TCAS)(TCAS)

Traffic Collision Avoidance System Traffic Collision Avoidance System (TCAS)(TCAS)

an aircraft collision avoidance system designed to an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between reduce the incidence of mid-air collisions between aircraftaircraft

monitors the airspace around an aircraft for other monitors the airspace around an aircraft for other aircraft equipped with a corresponding active aircraft equipped with a corresponding active transponder, independent of air traffic control, and transponder, independent of air traffic control, and warns pilots of the presence of other transponder-warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air equipped aircraft which may present a threat of mid-air collisioncollision

It is an implementation mandated by International Civil It is an implementation mandated by International Civil Aviation Organization to be fitted to all aircraft with Aviation Organization to be fitted to all aircraft with maximum take-off mass over 5700 kg or authorised to maximum take-off mass over 5700 kg or authorised to carry more than 19 passengers.carry more than 19 passengers.

TCAS involves TCAS involves communication communication between all aircraft between all aircraft equipped with an equipped with an appropriate appropriate transpondertransponder

Each TCAS-equipped Each TCAS-equipped aircraft "interrogates" aircraft "interrogates" all other aircraft in a all other aircraft in a determined range determined range about their, and all about their, and all other craft reply to other craft reply to otherother

it determines if a it determines if a potential collision threat potential collision threat existsexists

automatically automatically negotiating a mutual negotiating a mutual avoidance maneuver avoidance maneuver between the between the conflicting aircraftconflicting aircraft

avoidance maneuvers avoidance maneuvers are communicated to are communicated to the flight crew by a the flight crew by a cockpit display and by cockpit display and by synthesized voice synthesized voice instructionsinstructions

  Versions of TCASVersions of TCAS

A. PassiveA. Passive– Collision Avoidance Collision Avoidance

systems which rely on systems which rely on transponder replies transponder replies triggered by ground and triggered by ground and airborne systemsairborne systems

– generally have a range generally have a range of less than 7 nautical of less than 7 nautical milesmiles

B. TCAS IB. TCAS I– monitor the traffic monitor the traffic

situation around a plane situation around a plane (to a range of about 40 (to a range of about 40 miles) and offer miles) and offer information on the information on the approximate bearing and approximate bearing and altitude of other aircraftaltitude of other aircraft

– It can also generate It can also generate collision warnings in the collision warnings in the form of a "form of a "Traffic Traffic Advisory”Advisory”

– does not offer any does not offer any suggested remedysuggested remedy

  Versions of TCASVersions of TCAS

C. TCAS IIC. TCAS II– offers all the benefits of offers all the benefits of

TCAS ITCAS I– offer the pilot direct, offer the pilot direct,

vocalized instructions to vocalized instructions to avoid danger, known as a avoid danger, known as a "Resolution Advisory“"Resolution Advisory“

– TCAS II systems TCAS II systems coordinate their coordinate their resolution advisories resolution advisories before issuing commands before issuing commands to the pilotsto the pilots

– vertical separation vertical separation advisoriesadvisories

D. TCAS IIID. TCAS III– "next generation" of "next generation" of

collision avoidance collision avoidance technologytechnology

– had the capability to had the capability to offer traffic advisories offer traffic advisories and resolve traffic and resolve traffic conflicts using horizontal conflicts using horizontal as well as vertical as well as vertical manouevring directivesmanouevring directives

– currently suspended and currently suspended and there are no plans for its there are no plans for its implementationimplementation

TCAS LimitationsTCAS Limitations limited to supporting only vertical separation limited to supporting only vertical separation

advisoriesadvisories ATC isn't automatically informed about resolution ATC isn't automatically informed about resolution

advisoriesadvisories TCAS lacks automated facilities, increases pilot TCAS lacks automated facilities, increases pilot

workloadworkload Lack of terrain/ground awareness informationLack of terrain/ground awareness information TCAS is not fitted to many smaller aircraft mainly TCAS is not fitted to many smaller aircraft mainly

due to the high costsdue to the high costs

Radio Magnetic Radio Magnetic Indicator (RMI)Indicator (RMI)

Radio Magnetic Indicator (RMI)Radio Magnetic Indicator (RMI) displays aircraft heading and displays aircraft heading and

bearing to selected radio navigation bearing to selected radio navigation aids.aids.

Most RMI incorporate two direction Most RMI incorporate two direction needles. needles.

Typically, the thin, single-barred Typically, the thin, single-barred needle is connected to an needle is connected to an ADF/TACAN and the other thicker ADF/TACAN and the other thicker and/or double-barred is connected and/or double-barred is connected to a VOR. to a VOR.

Heading indicator – direction of the Heading indicator – direction of the aircraft in relation to magnetic northaircraft in relation to magnetic north

Bearing indicator – the actual Bearing indicator – the actual bearing to the stationbearing to the station

Ground Proximity Ground Proximity Warning System Warning System

(GPWS) / (GPWS) / Enhanced Ground Enhanced Ground Proximity Warning Proximity Warning System (EGPWS)System (EGPWS)

Ground Proximity Warning System Ground Proximity Warning System (GPWS) (GPWS)

Invention of Don BatemanInvention of Don Bateman alert pilots if their aircraft is in alert pilots if their aircraft is in

immediate danger of flying immediate danger of flying into the ground.into the ground.

Ground-Collision Warning Ground-Collision Warning System (GCWS)System (GCWS)

the system is purely reactive the system is purely reactive and can not look ahead at and can not look ahead at terrainterrain

can not always give pilots can not always give pilots sufficient time to predict and sufficient time to predict and plan avoidance maneuversplan avoidance maneuvers

A computer then keeps track of these readings, calculates A computer then keeps track of these readings, calculates trends, and will warn the captain with visual and audio trends, and will warn the captain with visual and audio messages if the aircraft is in certain defined flying messages if the aircraft is in certain defined flying configurations ("configurations ("modesmodes")."). Mode 1 - Excessive Decent Mode 1 - Excessive Decent

RateRate– Has two (2) boundaries and is Has two (2) boundaries and is

independent of vehicle independent of vehicle configuration. configuration.

Mode 2 - Excessive Terrain Mode 2 - Excessive Terrain Closure RateClosure Rate– Monitors airspeed, AGL Monitors airspeed, AGL

altitude and AGL rate-of-altitude and AGL rate-of-change, MSL altitude and change, MSL altitude and vehicle configuration. vehicle configuration.

Mode 3 - Altitude Loss After Mode 3 - Altitude Loss After Takeoff Or Rejected LandingTakeoff Or Rejected Landing– Provides an alert if a decent is Provides an alert if a decent is

made during initial climb or made during initial climb or climb after rejected landingclimb after rejected landing

Mode 4 - Unsafe Terrain ClearanceMode 4 - Unsafe Terrain ClearanceMode 4a - Clean ConfigurationMode 4a - Clean Configuration– terrain clearance mode with the gear terrain clearance mode with the gear

retracted and is armed after take off retracted and is armed after take off upon climbing through 215 upon climbing through 215 meters AGLAGL

Mode 4b - Landing Configuration Mode 4b - Landing Configuration – provides an alert when the gear is provides an alert when the gear is

down and the flaps are not in landing down and the flaps are not in landing positionposition

Mode 5 - Below Glideslope Deviation Mode 5 - Below Glideslope Deviation AlertAlert– alerts you of a descent of more than alerts you of a descent of more than

1.3 dots below an ILS glideslope1.3 dots below an ILS glideslope Mode 6 - Excessive Bank Angle For Mode 6 - Excessive Bank Angle For

AltitudeAltitude– alerts when descending through alerts when descending through

selected decision height with gear selected decision height with gear downdown

Enhanced Ground Proximity Enhanced Ground Proximity Warning SystemWarning System

the EGPWS displays the surrounding terrain (up to the EGPWS displays the surrounding terrain (up to 320 NM) on an EFIS screen or weather radar CRT, 320 NM) on an EFIS screen or weather radar CRT, and provides alerts about a minute's flight time or and provides alerts about a minute's flight time or more away from terrainmore away from terrain

On-board computers can compare its current On-board computers can compare its current location with a database of the Earth's terrain.location with a database of the Earth's terrain.

Pilots will receive much more timely cautions and Pilots will receive much more timely cautions and warnings of any obstructions to the aircraft's warnings of any obstructions to the aircraft's path.path.

The Black Box The Black Box

The Black BoxThe Black Box Although they are called "black boxes," aviation Although they are called "black boxes," aviation

recorders are actually painted bright orange.recorders are actually painted bright orange. Data from both the CVR and FDR is stored on Data from both the CVR and FDR is stored on

stacked memory boards inside the crash-stacked memory boards inside the crash-survivable memory unit (CSMU)survivable memory unit (CSMU)

The black box is powered by one of two power The black box is powered by one of two power generators that draw their power from the plane's generators that draw their power from the plane's engines. One generator is a 28-volt DC power engines. One generator is a 28-volt DC power source, and the other is a 115-volt, 400-hertz (Hz) source, and the other is a 115-volt, 400-hertz (Hz) AC power sourceAC power source

A. Flight Data RecorderA. Flight Data Recorder   first prototype FDR was produced in 1957 first prototype FDR was produced in 1957

by Dr David Warren by Dr David Warren typically double wrapped, in strong typically double wrapped, in strong

corrosion-resistant stainless steel or corrosion-resistant stainless steel or titanium, with high-temperature insulation titanium, with high-temperature insulation insideinside

Crash - Survivable Memory UnitCrash - Survivable Memory Unit

a cylindrical compartment on the recordea cylindrical compartment on the recorde device is engineered to withstand extreme heat, device is engineered to withstand extreme heat,

violent crashes and tons of pressure. In older violent crashes and tons of pressure. In older magnetic-tape recorders, the CSMU is inside a magnetic-tape recorders, the CSMU is inside a rectangular box.rectangular box.

Using three layers of materials, the CSMU in a Using three layers of materials, the CSMU in a solid-state black box insulates and protects the solid-state black box insulates and protects the stack of memory boards that store the digitized stack of memory boards that store the digitized informationinformation

Three Layers of Three Layers of Crash - Survivable Memory UnitCrash - Survivable Memory Unit

1. 1. Aluminum housing Aluminum housing - There is a thin layer of - There is a thin layer of aluminum around the stack of memory cards. aluminum around the stack of memory cards.

2. 2. High-temperature insulation High-temperature insulation - This dry-silica material - This dry-silica material is 1 inch (2.54 cm) thick and provides high-is 1 inch (2.54 cm) thick and provides high-temperature thermal protection. This is what keeps temperature thermal protection. This is what keeps the memory boards safe during post-accident fires. the memory boards safe during post-accident fires.

3. 3. Stainless-steel shell Stainless-steel shell - The high-temperature - The high-temperature insulation material is contained within a stainless-insulation material is contained within a stainless-steel cast shell that is about 0.25 inches (0.64 cm) steel cast shell that is about 0.25 inches (0.64 cm) thick. Titanium can be used to create this outer thick. Titanium can be used to create this outer armor as well. armor as well.

There are several tests that make up the crash-survival There are several tests that make up the crash-survival sequence: sequence:

1. 1. Crash impact Crash impact - Researchers shoot the CSMU down an air cannon to create an - Researchers shoot the CSMU down an air cannon to create an impact of 3,400 Gs (1 G is the force of Earth's gravity, which determines how much impact of 3,400 Gs (1 G is the force of Earth's gravity, which determines how much something weighs). At 3,400 Gs, the CSMU hits an aluminum, honeycomb target at a something weighs). At 3,400 Gs, the CSMU hits an aluminum, honeycomb target at a force equal to 3,400 times its weight. This impact force is equal to or in excess of force equal to 3,400 times its weight. This impact force is equal to or in excess of what a recorder might experience in an actual crash. what a recorder might experience in an actual crash.

2. 2. Pin drop Pin drop - To test the unit's penetration resistance, researchers drop a 500-pound - To test the unit's penetration resistance, researchers drop a 500-pound (227-kg) weight with a 0.25-inch steel pin protruding from the bottom onto the CSMU (227-kg) weight with a 0.25-inch steel pin protruding from the bottom onto the CSMU from a height of 10 feet (3 m). This pin, with 500-pounds behind it, impacts the CSMU from a height of 10 feet (3 m). This pin, with 500-pounds behind it, impacts the CSMU cylinder's most vulnerable axis. cylinder's most vulnerable axis.

3. 3. Static crush Static crush - For five minutes, researchers apply 5,000 pounds per square-inch - For five minutes, researchers apply 5,000 pounds per square-inch (psi) of crush force to each of the unit's six major axis points. (psi) of crush force to each of the unit's six major axis points.

4. 4. Fire test Fire test - Researchers place the unit into a propane-source fireball, cooking it using - Researchers place the unit into a propane-source fireball, cooking it using three burners. The unit sits inside the fire at 2,000 degrees Fahrenheit (1,100 C) for three burners. The unit sits inside the fire at 2,000 degrees Fahrenheit (1,100 C) for one hour. The FAA requires that all solid-state recorders be able to survive at least one hour. The FAA requires that all solid-state recorders be able to survive at least one hour at this temperature. one hour at this temperature.

5. 5. Deep-sea submersion Deep-sea submersion - The CSMU is placed into a pressurized tank of salt water - The CSMU is placed into a pressurized tank of salt water for 24 hours. for 24 hours.

6. 6. Salt-water submersion Salt-water submersion - The CSMU must survive in a salt water tank for 30 days. - The CSMU must survive in a salt water tank for 30 days. 7. 7. Fluid immersion Fluid immersion - Various CSMU components are placed into a variety of aviation - Various CSMU components are placed into a variety of aviation

fluids, including jet fuel, lubricants and fire-extinguisher chemicals. fluids, including jet fuel, lubricants and fire-extinguisher chemicals.

FDR Record ParametersFDR Record Parameters prior to September 30, 1969, record six flight prior to September 30, 1969, record six flight

parameters: altitude; airspeed; heading; vertical parameters: altitude; airspeed; heading; vertical acceleration; time of day; and the relative time of radio acceleration; time of day; and the relative time of radio transmissions to and from air traffic controllers. transmissions to and from air traffic controllers.

Airplanes certificated after that date were required to Airplanes certificated after that date were required to record a total of 11 parameters, adding to the list: pitch record a total of 11 parameters, adding to the list: pitch attitude, roll attitude, longitudinal acceleration, control-attitude, roll attitude, longitudinal acceleration, control-column position, and engine thrust indications. column position, and engine thrust indications.

Then, it had to record 17 parameters on any flight after Then, it had to record 17 parameters on any flight after May 25, 1994. The six additional parameters included: May 25, 1994. The six additional parameters included: pitch trim position; control wheel position; rudder pedal pitch trim position; control wheel position; rudder pedal position; position of each thrust reverser; trailing-edge position; position of each thrust reverser; trailing-edge flap position; and leading-edge flap position.flap position; and leading-edge flap position.

FDR Record Parameters FDR Record Parameters Currently, there are 88 parameters required as a Currently, there are 88 parameters required as a

minimumminimum a few of the parameters recorded by most FDRs: a few of the parameters recorded by most FDRs:

FDRFDR LocationLocation Black boxes are usually sold directly to and Black boxes are usually sold directly to and

installed by the installed by the airplaneairplane manufacturers. Black manufacturers. Black boxes are installed in the tail of the plane. The boxes are installed in the tail of the plane. The entire front of the aircraft acts as a "crush zone" entire front of the aircraft acts as a "crush zone" to reduce the shock that reaches the recorder. to reduce the shock that reaches the recorder. The precise location of the recorders depends on The precise location of the recorders depends on the individual plane. Sometimes they are located the individual plane. Sometimes they are located in the ceiling of the galley, in the aft cargo hold or in the ceiling of the galley, in the aft cargo hold or in the tail cone that covers the rear of the aircraft. in the tail cone that covers the rear of the aircraft.

Retrieving DataRetrieving Data With the data retrieved from the FDR, the Safety Board can With the data retrieved from the FDR, the Safety Board can

generate a computer animated video reconstruction of the generate a computer animated video reconstruction of the flight. flight.

The investigator can then visualize the airplane's attitude, The investigator can then visualize the airplane's attitude, instrument readings, power settings and other characteristics instrument readings, power settings and other characteristics of the flight. of the flight.

This animation enables the investigating team to visualize the This animation enables the investigating team to visualize the last moments of the flight before the accident.last moments of the flight before the accident.

Black boxes are also equipped with an Underwater Locator Black boxes are also equipped with an Underwater Locator Beacon (ULB). If a plane crashes into the water, this beacon Beacon (ULB). If a plane crashes into the water, this beacon sends out an ultrasonic pulse at 37.5 kilohertz (kHz) that sends out an ultrasonic pulse at 37.5 kilohertz (kHz) that cannot be heard by human ears but is readily detectable by cannot be heard by human ears but is readily detectable by sonar and acoustical locating equipment. There is a sonar and acoustical locating equipment. There is a submergence sensor on the side of the beacon that looks like submergence sensor on the side of the beacon that looks like a bull's-eye. When water touches this sensor, it activates the a bull's-eye. When water touches this sensor, it activates the beacon. computer animated video reconstruction of the flight. beacon. computer animated video reconstruction of the flight.

B. COCKPIT VOICE RECORDERB. COCKPIT VOICE RECORDER There may be up to four microphones in the plane's cockpit, each There may be up to four microphones in the plane's cockpit, each

connected to the cockpit voice recorder (CVR)connected to the cockpit voice recorder (CVR) Any sounds in the cockpit are picked up by these microphones and sent Any sounds in the cockpit are picked up by these microphones and sent

to the CVR, where the recordings are digitized and stored.to the CVR, where the recordings are digitized and stored.

There is also another device in the cockpit, called the associated control There is also another device in the cockpit, called the associated control unit that provides pre-amplification for audio going to the CVR. The unit that provides pre-amplification for audio going to the CVR. The positions of the four microphones are:positions of the four microphones are:1. Pilot's headset 1. Pilot's headset 2. Co-pilot's headset 2. Co-pilot's headset 3. Headset of a third crew member (if there is a third crew 3. Headset of a third crew member (if there is a third crew member) member) 4. Near the center of the cockpit, where it can pick up audio 4. Near the center of the cockpit, where it can pick up audio alerts alerts and other sounds and other sounds

Most magnetic-tape CVRs store the last 30 Most magnetic-tape CVRs store the last 30 minutes of sound. They use a continuous loop of minutes of sound. They use a continuous loop of tape that completes a cycle every 30 minutes. As tape that completes a cycle every 30 minutes. As new material is recorded, the oldest material is new material is recorded, the oldest material is replaced. CVRs that used solid-state storage can replaced. CVRs that used solid-state storage can record two hours of audio. Similar to the record two hours of audio. Similar to the magnetic-tape recorders, solid-state recorders magnetic-tape recorders, solid-state recorders also record over old materialalso record over old material

Retrieving DataRetrieving Data A CVR committee usually consisting of members A CVR committee usually consisting of members

from the NTSB, FAA, operator of the aircraft, from the NTSB, FAA, operator of the aircraft, manufacturer of the airplane, manufacturer of the manufacturer of the airplane, manufacturer of the engines, and the pilots union, is formed to listen to engines, and the pilots union, is formed to listen to the recording. the recording.

This committee creates a written transcript of the This committee creates a written transcript of the CVR audio to be used during the investigation. CVR audio to be used during the investigation.

The CVR records the flight crew's voices, as well as The CVR records the flight crew's voices, as well as other sounds inside the cockpit. other sounds inside the cockpit.

From the sounds, parameters such as engine rpm, From the sounds, parameters such as engine rpm, system failures, speed, and the time at which certain system failures, speed, and the time at which certain events occur can often be determined. events occur can often be determined. Communications with Air Traffic Control, automated Communications with Air Traffic Control, automated radio weather briefings, and conversation between radio weather briefings, and conversation between the pilots and ground or cabin crew are also recordedthe pilots and ground or cabin crew are also recorded