Avionics MCQs – ILS/MLS Coupled Landing System and Automatic Landing – 2

1 - Question

What is the beam error in localizer for aircraft CG displacement of 5m at a range of 1,500m?
Explanation: The beam error γ = d/R, where d is the displacement of the aircraft’s CG from the beam center line and R is the slant range of the aircraft. γ = 5/1,500 = 0.0033 RAD.

2 - Question

The guidance sensitivity decreases as the range decreases
a) True
b) False
Explanation: The beam error of a localizer or glide path transmitter is given by γ =d/R, Where R is the slant range of the aircraft. It is evident that the beam error is inversely proportional to the slant range. As range increases, beam error decreases and hence the guidance sensitivity is more.

3 - Question

When does an ILS localizer coupling loop become unstable?
a) Aircraft range is infinity
b) Aircraft range is close to zero
c) When too many aircraft are present
d) When no aircraft is present
Explanation: In the localizer coupling loop gain increases as range between aircraft and runway decreases. The gain reaches a point where it becomes too large and the loop becomes unstable. Thus gain scheduling with range is required.

4 - Question

What is missing in the localizer coupling loop?
a) Flight computer
d) ILS Localizer transmitter
Explanation: The Localizer coupling loop is integrated with the heading command loop to manage the heading of the aircraft. It is a closed loop system which continuously corrects with respect to the ILS Localizer. The error in flight path is corrected with respect to the localizer beam by means of a localizer receiver in the aircraft.

5 - Question

Which one of the following is not a basic parameter used to define visibility category?
a) Decision height
b) Minimum vertical visibility
c) Runway length
d) Runway visual range
Explanation: The two basic parameters used to define the visibility category are the decision height, that is the minimum vertical visibility for the landing to proceed and the runway visual range. The length of a runway is not used to define visibility category.

6 - Question

Which of the following is not one of the operational limits and autopilot requirement for a category IIIc visibility condition?
a) Runway guidance required to taxi point
b) Fully automatic landing system with flare
c) Probability of catastrophic failure of less than 10−7 per hour required
d) Decision height of 5m
Explanation: The autopilot requirements and operational limits for a category III visibility conditions are a probability of catastrophic failure of less than 10−7 per hour, fully automatic landing system with flare, runway guidance required to taxi point. The decision height for a category IIIc condition is 0m. No system is yet certified for category IIIc operation.

7 - Question

How is altitude measured when the aircraft is about to land?
a) Pitot static port
b) Pitot stagnation port
Explanation: When an aircraft is about to land, accurate altitude measurements are needed. Pitot static measurements suffer from errors due to weather and generally have lag. The aircraft height above the ground is measured by very accurate radio altimeters during the landing phase.

8 - Question

Why is flare maneuver executed during landing phase?
a) To align with the runway
b) To reduce airspeed and rate of descent
c) To stabilize the aircraft during crosswinds
d) To conserve fuel
Explanation: The flare maneuver is the increase in pitch of the aircraft seconds before touching the ground. This is done to reduce the airspeed and the rate of descent. If the flare is not executed correctly it may result in a runway overrun, landing gear collapse or a tail strike.

9 - Question

Why is the kick off drift maneuver executed?
a) To align with the runway
b) To reduce airspeed and rate of descent
c) To stabilize the aircraft during crosswinds
d) To conserve fuel
Explanation: Just prior to touchdown a ‘kick off drift’ maneuver is initiated through the rudder control so that the aircraft is rotated about the yaw axis to align it with the runway. This ensures the undercarriage wheels are parallel to the runway center line so that no sideways velocity is experienced by the wheels when they make contact with the runway.

10 - Question

What is HREF in the control law used for auto flare?
a) Height when flare is initiated
b) Height where flare should be initiated
c) Maximum height where flare can be initiated
d) Small negative height
Explanation: In the control law for auto flare, HREF is a small negative height, or bias, which ensures there is still a small downwards velocity at touchdown. This avoids the long exponential ‘tail’ to reach zero velocity and enables a reasonably precise touchdown to be achieved.

11 - Question

The final approach path in a satellite landing guidance can be curved
a) True
b) False
Explanation: Since GPS does not use radio beams to align the aircraft to the runway center line the final approach path need not be limited to straight line approaches, but can be curved or stepped, horizontally or vertically. The life cycle costs of a GBAS is also only a fraction of ILS or MLS.

12 - Question

What controls the efficient functioning of an engine?
a) Autopilot
b) FMS
c) FBW