4.1 NOTAMs, Wake Turbulence, and Altimeters

This lesson covers essential pre-flight knowledge, the invisible hazard of wake turbulence, and how your altimeter actually works.

NOTAMs (Notice to Airmen)

A NOTAM is a notice containing information about the establishment, condition, or change in any aeronautical facility, service, procedure, or hazard.

• Purpose: To provide timely knowledge essential to pilots. You must check NOTAMs as part of your pre-flight preparations.
• Scope: A NOTAM can apply to the entire country, a large area (for example, a military exercise or forest fire), or a single airport (for example, an airshow or temporary runway closure).
• Hang Gliding: Some hang glider sites request that NOTAMs be issued to alert the flying community that hang gliding activities are taking place.

You can find current NOTAMs on the NavCanada flight planning website.

Wake Turbulence (Causes, Effects, and Avoidance)

Wake turbulence is a hazardous by-product of lift caused by wing tip vortices. As a lift-producing wing passes through the air, the airflow rotates up and back from each wing tip, producing two distinct, counter-rotating vortices.

[Placeholder: Image - Vortex Core / Wake Turbulence Diagram]

Key Characteristics of Wake Turbulence

• When it happens: Vortices start when the aircraft’s nose wheel leaves the ground (rotation) on take-off, and continue until the nose wheel touches down on landing.
• Intensity: The heavier and slower the aircraft is, the greater the intensity of the vortex. Wake turbulence is usually most violent when large aircraft are climbing out from take-off or approaching to land.
• Movement: Vortices sink below and behind the generating aircraft. Because they drift with the wind, they are not always found directly behind the aircraft.

The Danger to Hang Gliders

Flight behind heavy aircraft may result in unresponsive controls, loss of control, and structural damage. This danger increases as the size and weight of your aircraft decreases. Therefore, all other aircraft produce hazardous wake turbulence for a hang glider. You should always avoid flying behind and below other aircraft.

The Altimeter

An altimeter is a special form of aneroid barometer (a barometer without liquid) which measures the pressure of the atmosphere. Because air pressure decreases with altitude, the barometer can be used to extrapolate your altitude.

Standard Air Conditions

Altimeters are calibrated based on “Standard Air Conditions” at sea level, which are:

• Temperature: 15ºC
• Air Weight: 14.7 lb per square inch
• Pressure: 29.92 inches of mercury (altitudes based on this setting are referred to as ICAO altitudes)

Correcting the Altimeter

Because air conditions rarely match “Standard” conditions perfectly, an altimeter will display an erroneous altitude unless it is corrected.

• Local Flights: Hang glider pilots correct this by setting their altimeter to display the actual take-off or LZ altitude before a flight.
• Cross-Country Flights: Because barometric pressure varies from place to place, an altimeter will display an erroneous reading after traveling some distance. Aircraft instruments have a barometric scale to calibrate the altimeter to local settings provided by a FIC/FSS or ATC unit.