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Few aircraft outside of the military are deliberately built
to provide the pilot with good visibility. Also, the cockpit
environment often causes the pilot to focus their
attention in the cockpit.
ATC Environment
If either or both of the aircraft were under air traffic
control, then ATC has some degree of involvement in
the collision.
Collision Avoidance Equipment
As more aircraft become equipped with TCAS equipment,
several questions are bound to arise.
• Was either aircraft TCAS equipped?
• If so, was the equipment functioning?
• Did the equipment provide the pilots with any
warning of the impending collision?
Runway Incursions
Runway incursions are usually associated with some
form of human factors contribution (See Lesson 14). In
addition, the following factors also contribute to runway
incursion accidents:
• Weather
• Cockpit environment
• ATC environment
LAX 1991 - This aircraft was cleared to land while at the same time
a SkyWest Metroliner was cleared to taxi into position and hold on
the same runway. The 737 did not see the SkyWest plane in time to
avoid the accident. ATC error...
Aircraft Accident Investigation 24
RECORDING EQUIPMENT
Aircraft Flight Recorders
Digital Flight Data Recorders (DFDR)
The development of digital FDRs improved both data
readout and readout accuracy. The recording medium
became Mylar tape and the recording parameters suddenly
became anything on the airplane that could be
measured and reduced to digital forms. DFDRs have the
capability to record at least 62 different channels or
parameters; the number of actual parameters is almost
infinite as one channel can be used for several different
parameters. The following key items are always included
in all DFDRs:
• Time
• Altitude
• Airspeed
• Heading
• Acceleration (vertical)
• Pitch attitude
• Roll attitude
• Radio transmission keying
• Thrust / power on each engine
• Trailing edge flap or cockpit control
Cockpit Voice Recorders (CVRs)
The CVR records on Mylar tape and is much easier to
install and maintain than the FDR; thus more aircraft
are likely to have them. Most CVRs usually have a
cockpit area microphone (CAM) usually mounted on
the overhead panel between the pilots. This is meant to
record cockpit conversation not otherwise recorded
through the radio or interphone circuits. The CVR usually
has a separate channel for each flight deck crewmember
and records everything that goes through those
audio circuits. It may also have a channel for the cabin
public address (PA) system. The recording is a continuous
30 minute loop tape which automatically erases and
records over itself. At no time is there more than 30
minutes of recording available which means that events
occurring before landing (or crash) are not recorded.
Other Recording Sources
• FAA Tower and Center Radio (audio) tapes
• FAA Radar tapes
• Flight Service Station tapes
• National Weather Service radar tapes
SOUND SPECTRUM ANALYSIS
What if we could detect the cause of aircraft damage
simply by listening to the sounds recorded in the cockpit?
Detecting damage to aircraft after an accident or
incident is conducted with the help of various tools and
analysis techniques. Cockpit Voice Recorder (CVR)
data is a useful tool that investigators use to obtain audio
information from the cockpit during the sequence of
flight. There are two types of sound that may be analyzed,
speech and non-speech audio information.
The CVR records audio information on 4 channels.
Non-speech information is recorded on channel 1 from
the Cockpit Area Microphone (CAM). The CAM records
thumps, clicks and other sounds occurring in the
cockpit other than speech. Channels 2 and 3 of the
CVR record speech audio information from the Captain
and First Officer’s audio selector panels. Channel 4
records the audio information from the jump seat/
observer’s radio panel.
How are CVR recordings analyzed? The answer:
sound spectrum analysis. Sound spectrum analysis is
a technique that compares the amplitudes of sounds,
and plots the distribution on a three-dimensional graph.
This type of analysis depicts changes or modulations in
sounds, and it can pinpoint the time when these changes
occur.
Sound spectrum analysis can be used for analyzing both
speech and non-speech audio information. Believe it or
not, non-speech sounds are highly important to the investigation
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