16. session: instruments, altimetry

Altimetry definition

The science that determines our vertical position with respect to a given surface or point

Why is knowledge on altitude important for the flight

• Avoidance of Controlled Flight Into Terrain (CFIT)

• Separation with other aircraft

• Some levels are more suitable than others in terms of

  • Efficiency

  • Safety: weather, avoiding turbulence and ice

Altitude definition

Vertical distance between the vehicle and Sea Level (AMSL)

AMSL stands for

Above Mean Sea Level

Height definition

Vertical distance between the vehicle and terrain (AGL)

AGL stands for

Above Ground Level

Elevation

The vertical position of a given obstacle placed on the surface of the Earth with respect to Sea Level

Which elements have a declared elevation?

• Aerodromes

• Certain thresholds

Radioaltimeter definition

An instrument that we use to measure height (vertical distance between vehicle and terrain)

How does the radioaltimeter work

• Using a transmitter that sends a signal downwards and expects an echo.

• When this echo is produced, the signal travels again upwards against the belly of the aircraft

• A receiver can write down a timestamp

• By measuring the difference of time between the meeting and receiving signals we can determine the distance between the aircraft and terrain, knowing that the wave is traveling at speed of light

Typical range of the altimeter, when important?

2500 ft, when next to the ground (during approach and take-off maneuvers)D

What does GPWS stand for

Ground Proximity Warning System

Radioaltimeter: connection with GPWS

• The radio altimeter is a basic input in the Ground Proximity Warning System

• The Ground Proximity Warning System will alert the crew when flying against an obstacle

• When measuring a decrease in the height of the aircraft without any other meaningful input, such as extending the landing gear or extending the flaps, then the Ground Proximity Warning System may alert the crew that it is inadvertently flying against an obstacle, such as a mountain.

• Radio altimeter is important during approach maneuvers (ILS approach)

Altimeters are

Barometers

Barometers definition

Instruments thatmeasure outside static pressure

Most important layers of atmosphere and its boundary

• Troposphere

• Stratosphere

• Tropopause

The instruments we will use will be calibrated using the…, so we will have

ISA atmosphere, errors

QFE stands for

The static pressure at a given point on the surface of the earth, typically a runway threshold

What is QNE

Vertical distance of aircraft and the ficticious 1013.2 mb

P at SL ISA
Pref= 1013.2 mb

Flight levels

measured in flight levels: 100s of feet

Transition layer definition

• The spacing between the Transition Altitude and Transition Level

  • T. Altitude lower than T. Level

• It has to have at least 1000ft

Transition limits

• Lowest (T. Level)

• Highest (T. Altitude)

Which transition changes every day, Altitude or Level?, Why?

Transition Level, because it’s a function of QNH

What is QNH

MSLP (Mean Sea Level Pressure)

The vertical separation lowers when

• Accuracy increases

• Ability increases

Minimum separation of

1000 ft

The higher the altitude/FL, the ___ the accuracy of the instruments/altimeter

lower

CVSM stands for

Conventional Vertical Aeparation Minimum

CVSM values

• 1000 ft for up to FL290

• 2000 ft for FL290 or above

RVSM stands for

Reduced Vertical Aeparation Minimum

Which FL where the most congested in the 1990s?

FL340 - FL400

RVSM values

• 1000ft up to FL410

• 2000ft if FL410 or above

To go from CVMS to RVSM

needs certification (aircraft, crew)

Even/Odd criteria

• Set a direction as even and the other one as odd

• Segment the odd and even flights in different FLs

• Above FL410 it can be confusing, careful!

in CVSM the Even/Odd criteria is more confusing

very inneficient

Level Bust definition, minimum of

• unauthorized vertical deviation on ATC clearance (Air Traffic Control)

• Minimum value

  • CVSM: more than 300ft

  • RVSM: more than 200ft

Causes of Level Bust

• Misunderstanding of read back in ATC clearance

• wrong selection of FL in cockpit

• misunderstanding of QNH QNE or the whole static ref P system

A Level Bust might induce a …

Airprox

Airprox definition

Air Proximity Incident: loss of separation between aircrafts

TCAS triggered

What does a variometer show, units?

Vertical speed, fpm

Artificial horizon

Instrument to measure the attitude of the plane (pitch and bank angle)

How does the artificial horizon work?

It has a spinning gyroscope inside, which maintains the rotation axis cte

PFD stands for

Primary Flight Display

PFD has

all the relevant information in terms of dynamic and navigation variables for the flight

what do PFD contain

• altimeter

• variometer

• compass

• artificial horizon

• anemometer

• autopilot selections, different flight modes

ND stands for

Navigation Display

ND shows

the relative position of the aircraft with respect to the selected route, with waypoints

Anemometry definition

the science behind the determination of the true airspeed of the aircraft (the speed of a/c wrt the mass of air around it)

the determination of TAS is strongly related to

the static pressure (Pt)