Altimeters Flashcards
What is height
Indication above ground level usually height above aerodrome. QFE set in Subscale
What is altitude
Indication above MSL. When QNH is set altimeter indicates altitude.
What is elevation
Vertical distance from a fixed point on Earths surface above MSL.
What can horizontal pressure variation do to altitude
Pressure varies horizontally. Pressure slopes downwards from high to low. When flying from an area of high pressure to low pressure indicated altitude will remain same but true altitude will reduce.
Low Pressure: True altitude< Indicated
High Pressure: True altitude> Indicated.
What is transition altitude
Altitude at or below which vertical position of an aircraft is referenced to QNH. Above transition altitude aircraft use the Standard pressure setting SPS for level flight. Important that all aircraft operate with same pressure datum in order to maintain separation,
What is the transition level
Transition level is lowest available flight level. As you descend to transition level you change from SPS to QNH.
Airspace between transition altitude and level is the transition layer.
What happens to altitude when changing from QNH to SPS
If QNH is above SPS then altimeter reading will increase and decreases if SPS is above QNH.
What is under-reading and over-reading.
Under-reading is when altimeter is indicating lower altitude than you actually are.
Over-reading is the opposite and is unsafe as it will show a greater difference between terrain than you actually are.
What is accelerated airflow
Flying over high ground will cause a drop in static pressure. Altimeter will over-read as it will show an increase in altitude.
What is temperature error
Temperature of air affects pressure lapse rate. Flying from high temp to low temp dangerous as pressure level is sloping down. True altitude is decreasing as altimeter is overreading. Altimeter is set to ISA lapse rate.
