Teaching and Learning Flying - Airplane Instrument Rating

Flight Instruments

DEFINITION

SAFETY FACTORS

• Proper altimeter setting necessary for safe terrain clearance and traffic separation
• Pitot heat in IMC (iced pitot tube and drain hole may cause ASI to act like ALT)
• Flying from high (temperature and/or pressure) to low, "look out below"
• Magnetic compass is backup heading indicator
• Electric TC provides backup bank information after vacuum system failure
• HI precesses (check/reset every 15 minutes, and starting IAP)

TOLERANCES

II. B. 1. Exhibit adequate knowledge of the elements related to applicable aircraft flight instrument systems and their operating characteristics to include
a. pitot-static
b. altimeter
c. airspeed indicator
d. vertical speed indicator
e. attitude indicator
f. horizontal situation indicator
g. magnetic compass
h. turn-and-slip indicator/turn coordinator
i. heading indicator
j. electrical systems
k. vacuum systems
l. electronic flight instrument display
II. C. Instrument Cockpit Check
1. Exhibit adequate knowledge of the elements related to preflighting instruments, avionics and navigation equipment cockpit check by explaining the reasons for the check and how to detect possible defects
2. Perform the preflight on instruments, avionics and navigation equipment cockpit check by following the checklist appropriate to the aircraft flown
3. Determine that the aircraft is in condition for safe instrument flight including
a. communications equipment
b. navigation equipment, as appropriate to the aircraft flown
c. magnetic compass
d. heading indicator
e. attitude indicator
f. altimeter
g. turn-and-slip indicator
h. vertical speed indicator
i. airspeed indicator
j. clock
k. power source for gyro instruments
l. pitot heat
m. electronic flight instrument display
n. traffic awareness/warning/avoidance system
o. terrain awareness/warning/alert system
p. FMS
q. auto pilot
4. Note any discrepancies and determine whether the aircraft is safe for instrument flight or requires maintenance

OBJECTIVES

PROCEDURES

Lecture/Discussion:
a. pitot-static system

1) Includes three basic pressure-operated instruments:
a) Sensitive altimeter
b) Airspeed indicator (ASI)
c) Vertical speed indicator (VSI)

2) Static (ambient) pressure


3) Pitot pressure (impact or ram air pressure)
4) Position error
b. altimeter

1) Aneroid barometer
2) Principle of operation
a) Evacuated, corrugated bronze aneroid capsules
b) Pilot adjustable barometric scale, visible in the Kollsman window
3) Altimeter errors
a) Preflight check for mechanical error: (75 feet)
b) Nonstandard temperature effects
c) Nonstandard pressure effects ("flying from high to low, look out below!")
4) Encoding altimeter
a) Mode C transponder
b) 125 feet
5) Absolute altimeter (radar or radio altimeter)
c. airspeed indicator (ASI)

1) ASI is a differential pressure guage that measures dynamic pressure
2) Indicated airspeed (IAS)
3) Calibrated airspeed (CAS)
4) Equivalent air speed (EAS)
5) True airspeed (TAS) (TAS = CAS, standard atmosphere at sea level)
6) Mach number (TAS:speed of sound)
7) Airspeed color codes:
• White arc: flap-operating range (from flaps-down stall speed to maximum airspeed with flaps down)
• Green arc: Normal operating range (from flaps-up stall speed to maximum airspeed in rough air)
• Blue radial line: Best single-engine rate of climb speed
• Yellow arc: Structural warning area (from maximum rough air speed to never-exceed speed)
• Red radial line: Never-exceed speed

d. vertical speed indicator (VSI) (vertical velocity indicator, VVI, rate-of-climb indicator)

1) Rate-of-pressure-change instrument
2) Static pressure and calibrated orifice
3) VSI lags behind actual pressure change, but more sensitive than alitimeter

e. attitude indicator (AI) (attitude instrument, artificial horizon, gyro horizon)

1) Gyroscopic rigidity in space
2) Operating mechanism: small brass wheel (gyroscope) with a vertical spin axis
a) Stream of air (via vacuum system) (C-TR182), or
b) Electric motor

3) Horizon disk fixed to gimbals remains in same plane as gyro
a) Pitch marks
b) Bank index
4) Symbolic aicraft mounted on instrument case over horizon disk
5) Erection mechanism (2 to 5 minutes)
6) Older gyros caging mechanism
7) Errors
a) Slight nose up or down during rapid acceleration or deceleration respectively
b) Possible small bank and pitch errors after 180 degree turn
c) Errors are small and correct themselves within a minute or so in SLF
f. horizontal situation indicator (HSI)

1) Combines magnetic compass (or HI) with navigation signals and glide slope
2) Heading indicator component usually driven by output from a flux valve
3) Displays location relative to selected course


g. magnetic compass
1) Operating principle - free magnets align with the earth's lines of flux
2) Required by 14 CFR part 91 for both VFR and IFR flight
3) Components
a) Two small magnets
b) Metal float
c) Clear fluid
d) Graduated scale, the card
e) Lubber line reference
f) Jewel-and-pivot type mounting
g) Compensator assembly
4) Compass errors
a) Variation
MC = TC + West Variation
MC = TC - East Variation
b) Deviation
i) Caused by local magnetic fields within the aircraft
ii) Recorded on compass correction card
c) Compass course (CC)
True course (TC) corrected for variation (V) and deviation (D)

TC +/- V = MC +/- D = CC
d) Dip errors
i) Northerly turning error
NOSE ("North Opposite, South Exaggerates")
ii) Acceleration error
ANDS (Accelerate North, Decelerate South)
e) Oscillation error
h. turn-and-slip indicator/turn coordinator (TC)
1) Principle of gyroscopic precession
2) Turn-and-slip indicator (needle and ball, turn-and-bank indicator)
3) Turn coordinator

a) Inclinometer (slip-skid indicator, coordination ball)
i) Indicates relationship between bank angle and rate of yaw
ii) Centered ball indicates coordinated turn
b) Turn indicator

i) Gyro gimbal frame angled upward about 30° allowing it to sense both roll and yaw
ii) Wing of symbolic airplane pointing to mark indicates standard rate turn
i. Heading indicator (HI, directional gyro, DG)
a) HI gyroscope
i) Double gimbal mounted
ii) Horizontal spin axis - senses rotation about aircraft vertical axis
iii) Rigidity in space causes HI to maintain heading indication without the oscillation and other errors inherent in the magnetic compass
b) Must be periodically (every 15 minutes) set to the heading indicated by the magnetic compass
c) Usually air-driven by vacuum system

j. electrical systems

C-TR182: turn coordinator gyroscope is electrically driven
Direct battery current
Independent of alternator (and vacuum system)
Other flight instruments function without electricity
HSI often electric
Back-up electric vacuum pump (in event of engine-driven vacuum pump failure)
k. vacuum systems

AI and HI gyros driven by engine-operated vacuum pump
Monitor suction gauge (4.5 - 5.4 inHg)
Additional back-up electric vacuum pump recommended
Cessna TR182 vacuum system
l. electronic flight instrument display (electronic flight instrument system, EFIS, "glass cockpit")
Garmin G1000, for example:



Elements
Primary flight display (PFD)
AI
HI
ASI
ALT
VSI
Inclinometer (slip/skid indicator)

Navigation display
Heading information
Route and course deviation on moving map
Digital bearing and distance to fix, ETE, ground track, ground speed, etc
Engine indicating and crew alerting system (EICAS)
Engine operation
Irregular conditions
Multi-function display (MFD)
Status of aircraft systems
Other optional information (weather, TCAS info)
Operate according to manufacturers recommendations and POH supplements

Preflight instrument check
a. communications equipment
b. navigation equipment, as appropriate to the aircraft flown
c. magnetic compass
d. heading indicator
e. attitude indicator
f. altimeter
g. turn-and-slip indicator
h. vertical speed indicator
i. airspeed indicator
j. clock
k. power source for gyro instruments
TC - electric/ammeter/low voltage light
AI and HI - vacuum/suction guage/low-vacuum warning light/backup electric vacuum
l. pitot heat (and prop deice)
Ammeter indication
Heat
m. electronic flight instrument display
Check according to manufacturers recommendations in POH supplements
n. traffic awareness/warning/avoidance system
Check according to manufacturers recommendations in POH supplements
o. terrain awareness/warning/alert system
Check according to manufacturers recommendations in POH supplements
p. FMS
Check according to manufacturers recommendations in POH supplements
q. auto pilot
Check according to manufacturers recommendations in POH supplements
For example C-TR182 checklist for S-TEC 60

COMMON ERRORS

• Failure to study POH for details of operation of instruments in a specific aircraft
• Failure to complete preflight instument check
• Failure to detect instrument defects

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