Instruments Flashcards
What is mach number?
The ratio of the speed of a body (TAS) to the local speed of sound in the surrounding medium
What is Mcrit?
The speed at which a loss of control occurs due to shock waves forming, because the IAS this happens at changes with change in temp we use Mach
What are the types of airspeed and what are they accounting for?
IAS
CAS - position and instrument
EAS - compressibility
TAS - density
What is VMO?
Maximum operating speed (same as Vne)
What is mach tuck? why does it occur?
Nose down pitch due to a rearward movement of the CoP
Sound waves are generated from the aircraft, due to its movement the waves in front of the ac begin to bunch up and eventually cannot travel faster than the ac. The waves superimpose on themselves and a shockwave forms.
What does a Machmeter consist of?
Altimeter and Airspeed Indicator
What is the speed of sound a function of? what is the relationship?
Temperature. Increase temperature, increase local speed of sound.
What is the ratio that the machmeter uses to indicate mach?
M = dynamic pressure (pitot-static)/static pressure
What errors is the machmeter subject to?
Instrument error - due to friction, 0.01M between 0.5-1.0M
Pressure (Position) error - static pressure is used twice so any static pressure errors are accentuated, can affect ADC if the area around the static port is corrupted
Blockages - static or pitot pressure will affect the readings, static blockage will result in the MM reading low in the climb and vice versa
What should the Machmeter read before flight?
Zero
What has replaced the need for mechanical machmeters?
ADCs
What are the inputs and outputs of the ADC?
Inputs:
Pitot pressure
Static pressure
OAT
AOA
Outputs:
Altitude
Vertical speed
CAS
TAS
Mach
VMO
AOA
TAT - total air temp
SAT - static air temp
What units receive ADC info?
PFD - PIC and CoP
AFDS
Altitude encoding -SSE
EGPWS/TAWS
Auto throttle
Yaw damper - for rudder restrictions
Cabin pressurisation
FDR
What are the typical altitude alerts from the ADC/RADALT?
1000ft to go
- alt black text (ALT ALERT)
- aural tone
- flashes 5 secs
200ft to go
- alt blue text (ALT ALERT)
- flashes 5 secs
Deviation of 200ft from assigned
- master caution, yellow text (ALT ALERT)
- aural tone
- flashes 5 secs
What are the 3 advantages of EFIS?
Versatility
Flexibility
Redundancy
What is a stick shaker? What does it do?
Mechanical device, normally attached to shaft of control column, physically shakes one or both of the control columns at high frequency to warn crew of an impending stall.
What creates the stick shaker vibration?
A small electric motor that rotates an out of balance rotor
How does the stick shaker know when the aircraft will stall? Is it airspeed?
No. Various inputs into stall warning computer determines the stall speed depending on given config. Pitch limit indicator displayed on the EADI/PFD, staying below them will avoid stall/stick shaker activation
What are the physical requirements of the CVR?
Bright orange or yellow
Reflective tape
Underwater locating device
What length of recording are CVRs required to store?
Minimum 2 hours
How do RADALT function?
Frequency modulation, a transmitter sends out a continuous wave FM signal toward the ground between 4250-4350 MHz (SHF), it is reflected off the ground and received by the receiver. The relationship between frequency of the transmitter and the receiver at any one time relates to a change in height (40Hz per ft).
How is the RADALT stopped?
WOW pacification (SHF on ground is dangerous), auto shutdown at upper altitude
What altitude and surface is RADALT best at?
2500ft and below, better over the ocean than the ground
What colour are the master warnings? (4)
Time critical warnings;
Warnings - red
Cautions - amber
Advisorys - amber indented
Comms alerts/memo - white
Status message cue - cyan
What configurations will the master warning/caution reset switch not function?
Autopilot disc
T/O/LDG config
Overspeed warning
What are the disadvantages of first gen GPWS?
Does not scan ahead of the aircraft so a GPW may not alert for flight toward sheer terrain or a slow descent in ldg config into terrain
What are the 7 GPWS modes? what alt do they function from? which are selected automatically?
1 - Excessive descent rate
2 - Excessive terrain closure
3 - Alt loss after t/o or go around
4 - unsafe terrain clearance at high speed or not in landing config
5 - Below GS deviation
6 - RADALT/bank angle protection
7 - Reactive wind shear
all below 2,500ft radalt
Mode 3+4
What does EGPWS use to provide forward facing alerts?
world wide digital terrain database with GNSS position
How does the remote vertical gyro maintain its spin axis?
Erection system using mercury switches (one in pitch and one in roll)
Torque motors are used to apply precessing forces, pitch erection torque motor applies force to roll axis, roll erection torque motor applies force to pitch axis
How do mercury switches work?
Sense a tilt away from vertical, makes electrical contact completing a circuit which results in tilt motors driving remote vertical gyro to vertical.
What are accelerometers? How do they work?
Used on INS/IRU stable platform to measure aircraft movements
3 used for the 3 axis
When the aircraft moves the acceleration loads a crystal and a millivoltage is produced in proportion to the acceleration
What are ring laser gyros? What do they sense? How do they work?
Solid state square or triangle device which senses rate
Block has 2 accurately drilled cavities, mirrors at each corner (one partially transparent), and is filled with a voltage applied helium or neon gas which produces light/laser beams of 2 opposing directions
Light has a frequency (sine wave) which will be in phase between the two beams, when the block rotates the distance the light travels will be altered creating a phase shift (difference) which is measured as a fringe pattern on the sensor and converted to an amount and rate of rotation
What is the purpose of the INS?
Provide a continuous and accurate fix of the aircraft position and steering command to the AFDS to navigate the aircraft via waypoints without external aid
INS main components?
Gyro stable platform, gyros keep platform aligned in azimuth and to true north, up to 3 for redundancy
Up to 3 accelerometers on platform, 1 N-S, 1 E-W, and maybe 1 vertical accel/alt (PRIMARY INS INPUT)
INS Computer, up to 3 for redundancy, receives accelerometer data to update nav memory, displays aircraft track on moving map, connected directly to AFDS
How does INS operate?
Newtons 1st law - rest unless force acted
A minimum of 2 accelerometers mounted on the stable gyro platform measure size, direction, and duration of aircraft movement
Computer tracks aircraft position using calculus, determining velocity via the 1st integral and distance travelled by the 2nd integral, also provides a heading.
What is the effect of the earth rotation on INS? What is required for this?
Rotation effects acceleration, software contains a counter for this and for imperfections on the earth surface.
Software requires 28 day updates
What is MEMs?
Micro electrical mechanical system gyro, solid state silicone device which measures aircraft movement
The vibrating structure is affected by Coriolis force as the aircraft moves, the movement changes the characteristics of the structure, detected as a change in electrical current
Alternate to RLG/replaces INS
How many parameters does a FDR record? Give an example
48-300 depending on aircraft/FDR age, altitude, heading, speed, load factor, engine readings
What powers the FDR?
The essential bus
How long does the FDR record for? Can it be erased?
minimum 25 hours, no
How are FDR recordings accessed?
With a laptop and specific programme/cable in manufactures lab
What is the FDR equipped with so it can be found?
Acoustic underwater locator beacon
What does a CVR record?
Everything.
Crew/ATC conversations
Engine sounds
Noise from aircraft systems
What powers the CVR? When can it be erased?
Essential bus
When WOW it can be erased
How long does the CVR record?
minimum 2 hours
What are the 2 components to FANS?
CNS - communication, navigation, surveillance
ATM - Air traffic management, using comms/surveillance
What is ACARS? What does it do?
Aircraft communication, addressing and reporting system
Provides comms between a/c and the ground via datalink, eliminates voices comms
What is SATCOM used for? What does it use?
long range voice comms and datalink, uses ACARS. Air-ground-air comms using satellites/ground stations to provide world wide coverage.
Uses geostationary satellites, L-band (1-2GHz)
