ILS/MLS Flashcards
What does ILS mean?
Instrument Landing Systems
What does MLS mean?
Microwave Landing Systems
What is ILS/MLS used for?
they are designed to allow the flight crew the ability to land the aircraft with the aid of the instrument references
What is Decision Height?
if enough of the airport environment is visible to safety land
What is a Missed Approach?
If conditions are too bad they will pull up and try again
The ILS has three categories or subdivisions. What is Category 1?
Category 1 - the most common
200ft decision height and RVR of 2400 ft
What does RVR stand for?
Runway Visual Range
The ILS has three categories or subdivisions. What is Category 2?
international and large airports
Decision height 100ft
RVR 1200ft
CAT II requires the airplane to have what?
a second localizer and glide scope receiver and a Radar Altimeter
Category III is divided into subdivisions A, B, and C, with Decision Height and RVR decreasing each subdivision. What is Category III sub division C?
This is a fully blind landing. Conditions are zero-zero. No decision height and no RVR
What 3 separate systems is the ILS based around?
Localizer
Glidescope
Marker Beacons
What does the Localizer Provide?
provides a directional reference to the left and right of the center line or a horizontal reference
What does the glidescope provide?
provides vertical directional service
What do marker beacons provide?
provide the known distance points from the end of the runway for the pilot to help determine how knit only where they are in approach but also aid in decision height or RVR conditions
What does the ILS localizer consist of?
two RF transmitters and eight loop antenna array
A signal to the right of the localizer path will be modulated with what frequency?
150Hz
A signal to the left of the localizer path will be modulated at what frequency?
90Hz
The localizer receiver in the aircraft does what?
discriminates between the 90 and 150Hz
What frequencies does the localizer operate in?
VHF navigation frequencies below 112.00MHz
The frequencies used with the localizer have what when in the 100KHz position?
Odd numbers
The localizer station transmits an audio ID for the pilot to verify the correct station. How is this ID received?
in Morse Code and always begins with the letter i
Because there is only one inbound course when in the localizer mode, the OBS (or course selector) is:
inoperative and there is no “to/from” indication
On the front course: the needle shows:
the direction that the nose of the aircraft needs to move in to get back on course
In localizer mode, and indicator must never:
display a “from”
What if an indicator displays “from”?
there is a malfunction in the system
Localizer signals are adversely affected by:
tall buildings and mountains
The VOR composite has:
30Hz, plus the continuously changing 9960Hz reference frequency
What are converters used for?
to change the composite signal into voltages that can be displayed on an indicator
What is the discriminator used for?
to extract the 30Hz reference signal from the 9960Hz sub-carrier
As the pilot turns the OBS, what does the resolver do?
delays the signal to introduce a phase change
The VOR station is referenced to:
Magnetic north
The resolver is connected to:
the OBS knob
The resolver allows the pilot to change:
the reference to any desired bearing
The L/R circuit is a phase comparator. If the variable and reference signals are 90 degrees apart, then the needle will be:
centered
The To/From circuit works almost the same as the Left/Right, but:
a 90 degree phase change is placed into the variable signal
The polarity of the To/From circuit output depends on:
what her the variable signal leads or lags the reference signal
If both signals are present (90Hz and 150Hz), the flag driver will:
produce up to 300mV to pull the fault flag out of view
Do VHF ILS antennas transmit?
No
The The VHF ILS Nav antennas are balanced and the transmission line leading to the receiver is not. What is required?
A Balun
What is a Balun?
a transformer designed to match an unbalanced transmission line to a balanced antenna
The marker beacon system is used to:
mark specific points in the ILS approach path to a runway
The marker beacons are ground based stations that transmit what?
an amplitude modulated signal on 75MHz
What happens as the aircraft passes over the marker beacon stations?
The light on the marker beacon system will illuminate and the audio tone will sound
In light aircraft, the Marker Beacon system may be part of the:
VOR/LOC receiver or Glide Slope Receiver
The location for the marker beacon antenna is:
on the bottom of the fuselage
The glide slope sends what kind of pattern?
Vertical
The Glide Slope uses what signals?
90Hz and 150Hz
What do the different Glide Scope signals determine?
The 150Hz signal is the lower half of coverage and the 90Hz is the signal for the upper range
The intended approach track provides an approach angle of:
2.5 to 3.5 degrees
Each of the 40 UHF frequencies is paired to:
a localizer frequency
On the aircraft indicator, if the aircraft is above the glide path:
the needle moves down
On the aircraft indicator, if the aircraft is on the glide path:
the needle is centered
On the aircraft indicator, if the aircraft is below the glide path:
the needle will move upward
The Glide Slope information can be displayed on what?
a dual needle CDI, HIS, HUD, or EFIS screen.
A RMI cannot display glide scope info
When will a pilot not have glide scope use?
when making a back way approach
Some approaches require what on the aircraft in order to perform the approach?
Distance Measuring Equipment (DME)
Testing the localizer requires:
simulating the localizer ground station with a test generator, then changing the signals to text the various outputs and indications
What should the aircraft be connected to when testing the localizer?
external power to avoid running down the battery
The glide scope receiver does not have what?
an audio output or it’s own control head
Triplexers have three outputs:
one for glide scope and two for the Nav receivers
Standard deflection for VOR is:
10 degrees of error
While testing the VOR accuracy, watch the RMI as well. The RMI should be:
+/- two degrees
The technician who certifies the aircraft must also be:
certified to perform the check
A benefit of MLS is:
the shorter wavelengths
How long are microwave signals in full wavelength?
2.5 inches
Having a smaller wavelength results in:
smaller antennas and signals that are easier to form into a narrow beam that can be steered electronically
What is known as the Azimuth function?
the measuring of the amount of time between the two beams and calculating where the aircraft is with respect to the runway, via the receiver
What can MLS support that ILS cannot?
a curved approach
What happened in 1978?
ICAO adopted MLS as the world standard for landing systems
Who were one of the first extensive user of MLS for aircraft operations?
NASA with the space shuttle program
What is an automatic feature that MLS can perform?
Auto land
What is the Multi-Mode Receiver (MMR)?
a modular system that operates ILS, MLS, and GLS (Glide Scope Landing system)
When the radio is tuned to one of the landing services, the pilot sees:
the same guidance information on the aircraft instrumentation
