CVR and FDR

Cockpit Voice Recorder (CVR) and Flight Data Recorder (FDR):

Cockpit Voice Recorder (CVR):
Cockpit Voice Recorders, often known as CVRs, are required equipment in all
commercial aircraft operating throughout the world. These devices record conversations
throughout an aircraft's cockpit on (in older models) digital tape and (in newer models) on a digital microchip. Sounds are picked up via a system of cockpit microphones, known as Cockpit Area Microphones (CAM), Public Address Microphones (PA), and radio microphones (RDO). In the event of an accident, this information may be used by investigators to determine what was occurring in the cockpit throughout the incident. A CVR is carefully engineered to withstand the force of a high speed impact and the heat of an intense fire. CVR is painted with high resistant orange paint for high visibility in the wreckage. CVR is also equipped with Underwater Locator Beacon (ULB) to assist in the event of an overwater accident. The device is called PINGER, is activated when the recorder is immersed in water. It transmits an emergency signal which then picked up by special receivers.

Flight Data Recorder (FDR):
Flight data recorder records the parameters of the aircraft during flight. By the rules
of ICAO an aircraft must record eighty eight (88) parameters. These parameters involves
altitude, air speed, heading and aircraft attitude. FDR can aid the air crash investigators in
many great ways. The data recovered from the FDR can be used to generate a computer
animated video reconstruction of the flight. FDR is also equipped with the same safety
components which are used in CVR.

Primary Flight Controls

Before knowing the primary flight controls one should know how an aircraft takes flight. What part does the wings play and what other surfaces do.

When it comes to the flying of an aircraft there is a difference between the engine and the wings. Most people think engine does most of the things and helps the aircraft to fly. The engine is one part of the aircraft. An aircraft’s engine is designed to make it move forward at high speed. While the wings of an aircraft moves it upward. The wings create an upward force called lift that overcomes the plane’s weight and hold it in the sky while the engine produces the force thrust and reducing the drag. Now the question arises, how do the wings provide the lift? Airplane’s wings have a curved upper surface and flat lower surface, making an airfoil (aerofoil) shape. When an aircraft moves forward the air that strike splits up. When air rushes over the curved surface of the wing it has to travel further at slightly higher speed than the air that passes underneath the surface. According to Bernoulli’s Law, pressure is inversely proportional to the speed, so the fast moving air is at low pressure than the slow moving air. In other words, the pressure at curved surface of the wing is low and the pressure is high underneath. This difference of pressure basically creates the lift for the aircraft. But according to Newton’s 3rd law of motion, if air gives an upward force, the plane must provide an equal and opposite force. The wings are technically designed to push the air downward so as to create an opposite force. The wings aren’t flat underneath but tilted so as to direct the air downward. Vertical and horizontal stabilizers are used to make the aircraft stable when it is lifted from the ground. 

An aircraft in flight is free to rotate in three dimensions: pitch, nose up or down about an axis running from wing to wing; yaw, nose left or right about an axis running up and down; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as lateral, vertical, and longitudinal.

STABILIZERS:

Vertical and horizontal stabilizers are installed to make the aircraft stable.

 
Vertical Stabilizer:
Vertical stabilizer keeps the airplane lined up with its direction of motion. Air presses
against both its surfaces with equal force when the airplane is moving straight ahead. But if the airplane pivots to the right or left, air pressure increases on one side of the stabilizer and decreases on the other. This imbalance in pressure pushes the tail back into line.

 

Horizontal Stabilizer:
The horizontal stabilizer helps keep the airplane aligned with its direction of motion. If the airplane tilts up or down, air pressure increases on one side of the stabilizer and decreases on the other, pushing it back to its original position. The stabilizer also holds the tail down, countering the tendency of the nose to tilt downward—a result of the airplane’s center of gravity being forward of the wing’s center of lift.

 

AILERON, ELEVATORS and RUDDER:
They are the primary controls of the aircraft.

Ailerons:
The movement of aileron is not symmetrical but opposite. When the pilot moves the aircraft left, aileron on the right wing is lowered and the opposite on the other aileron on the left wing. The pressure is increased on the lower side and the pressure is decreased on the other side making the aircraft tilt on the left side.

Elevators:
Unlike ailerons whose movement is not symmetrical, elevators movement is symmetrical. When the pilot pitches up the plane the elevators are moved up increasing the pressure at the tail. The tail is lowered and the nose of the plane is moved up thus pitching up the plane. 

Rudder:

The rudder is a fundamental control surface which is typically controlled by pedals rather than at the stick. It is the primary means of controlling yaw—the rotation of an airplane about its vertical axis. The rudder may also be called upon to counter-act the adverse yaw produced by the roll-control surfaces.

Radars

Introduction:
Radar is an object detection system that works on radio waves used to determine angle, velocity and range. It can be used to detect aircraft, airships, missiles, weather formations and terrain. The first radar was invented in World War II for military purpose now it is being used by civil aircraft as well. There are two basic types of radar; primary and secondary.  

Primary Radar:

The first radar that was developed was primary radar. Primary radars work on reflections i.e. an electromagnetic wave(radio wave) is transmitted and is reflected back by an object which is then received. It is used to find the distance. The total time of the radio wave is measured which is then multiplied by the speed of radio wave (radio waves travel with speed of light). The time which is measured is the total time i.e. transmitted and received, only the received time is required so it is divided by 2.

Primary radar on an aircraft:

Weather Radar:

Weather Radar is used to locate precipitation, its motion and its type (rain, snow etc.). Weather Radar sends directional pulses, the transmitted pulses are then reflected back and the total time for the pulses to return is measured and the distance is calculated. Radar returns are basically described by the colors or levels. There are three levels:
Level 1: corresponds to a green radar return, indicating light precipitation and a little turbulence.
Level 2: corresponds to a yellow radar return, indicating moderate precipitation, low visibility and moderate turbulence.
Level 3: corresponds to a red return, indicating heavy precipitation, possibility of thunderstorms and severe turbulence. This can also damage aircraft.

Low Range Radio Altimeter (LRRA):

A radio altimeter is an airborne electronic device capable of measuring the height of the aircraft above terrain immediately below the aircraft. The picture below is the display of LRRA.

Secondary Radar:
Unlike primary radars that are reflection based radars, secondary radars work on the concept of point to point communication. Secondary radar sends out a signal and rather than receiving the reflected signal, the transmitted signal interrogates the receiving vehicle, which then responds automatically some useful
information. This information can tell the height and position of the aircraft, its status etc.

 

Distance Measuring Equipment (DME):

DME allows the aircraft to measure the distance from a ground reference. The distance is determined by measuring the propagation and delay of a RF pulse, which is emitted by the aircraft transmitter and returned at a different frequency by the ground station after reception. When a signal is transmitted, DME starts counting the time until it gets a reply from the ground station. The time measured is then used for the calculation of the distance between the ground and the aircraft. The display of DME is shown in below picture;

 

Traffic Collision and Avoidance System (TCAS):

Collision Avoidance System is basically the communication between two aircraft to avoid any accident. It transmits a signal which is then received by another aircraft. The received signal interrogates the aircraft which then responds providing its information about the altitude and speed. There are 3 types of TCAS out of which only 2 are used.

1. TCAS I: It assists the crew visually location and identifying an intruder aircraft by issuing traffic advisory (TA).
2. TCAS II: It not only provides traffic advisory but also provides vertical flight manoeuvre guidance to the crew in the form of resolution advisory (RA). Resolution advisory aids the pilot in maintaining the vertical separation between the aircraft.
3.  TCAS III: It was intended to give pilot lateral guidance in addition to RA and TA, but the idea was suspended and was replaced by ADS-B (Automatic Dependent Surveillance - Broadcast).