Hazards
Thunderstorms
Thunderstorms pose a major risk to all aircraft, with a high likelihood of heavy precipitation, hail, strong & gusty winds, and severe turbulence. Large thunderstorms can create strong microbursts with downdrafts exceeding the climb capability of most aircraft.
Pilots should ensure they utilise their aircraft's weather radar (if equipped) and avoid sharp, contouring returns by a safe distance (generally 10nm at lower levels, up to 30nm at higher levels). See Radio Telephony for phraseology guidance.
If a thunderstorm is present within 5nm of your intended approach or departure path, you should delay commencing the approach or the takeoff roll. Ensure that you communicate these requirements with ATC as soon as possible, as there are likely significant coordination and separation assurance requirements which will need to be conducted to provide you with a particular clearance.
Icing
Different operators and aircraft manufacturers define icing conditions differently, however a common marker is the presence of visibile moisture (rain, cloud, mist, etc) with an OAT of 5°C or below. When ice forms on an aircraft, it can add significant weight (sometimes exceeding the aircraft's MTOW). Ice forming on the wings and other aerofoils can disrupt laminar airflow and cause a large decrease in the amount of lift produced. This effect is extended to propellers and rotor blades, which will see a significant reduction in thrust as a result.
Ice generally (but not always) forms in fixed temperature bands, with icing possible between 0°C and -40°C. The most common icing bands are below:
| Temperature Range | Ice Type | Hazard |
|---|---|---|
| 0°C to -10°C | Clear Ice | Large amount of added weight, aerofoil airflow disruption |
| -10°C to -20°C | Rime Ice | Aerofoil airflow disruption, small amount of added weight |
| -10°C to -15°C | Mixed Ice | Combination of Clear & Rime Ice |
Ice Protection Systems
Aircraft which regularly operate in these icing bands are generally equipped with ice protection systems. Anti-ice systems prevent the formation of ice by heating or otherwise treating aircraft surfaces. De-ice systems remove ice once it has formed by heating, expanding, or otherwise treating aircraft surfaces.
Pilots should be aware of the presence of forecast severe icing (through SIGMETs and SIGWX/GAF charts) and, if necessary, plan an amended route which avoids high terrain and would facilitate descent below the freezing level if severe icing is encountered. Pilots of aircraft which are not equipped with ice protection must not plan to enter visible moisture above the freezing level.
Warning
No aircraft is certified to operate in severe icing. Should severe icing be encountered, pilots must take action to leave the area as soon as practical.
Windshear/Wake Turbulence
Whilst simulators have traditionally not modelled the effects of windshear and wake turbulence on aircraft, newer generation software is starting to replicate this hazard.
ATC will apply the following wake turbulence separation between successive departures, however pilots should inform ATC as soon as possible if a longer delay is preferred.
| Lead Aircraft | Following Aircraft | Time (min) | Distance (nm) |
|---|---|---|---|
| Super | Heavy | 2 | 6 |
| Medium | 3 | 7 | |
| Light | 3 | 8 | |
| Heavy | Heavy | - | 4 |
| Medium | 2 | 5 | |
| Light | 2 | 6 | |
| Medium | Light | 2 | 5 |
Avoidance/Mitigation
Where windshear is known or forecast, pilots should mitigate its effects during takeoff by:
- Using the longest runway available or choosing the most into wind runway
- Using a lower flap setting
- Using a higher takeoff power setting
- Rotating at the normal predetermined speed
- Where performance allows, sacrificing initial climb gradient for increased IAS
During approach and landing, windshear can be mitigated by:
- Using a runway which minimises exposure to the windshear
- Increasing the aircraft's approach speed value
- Using a lower flap setting
- Avoiding large reductions in power until approaching the flare
Mountain Waves
Turbulent airflow with strong downdrafts can be present in the lee of mountain ranges when certain conditions are met. This can create a strong hazard to small aircraft, which may not be able to outclimb the sinking air.
Note
Mountain waves are unlikely in most simulators, however with the introduction of next generation software which replicates the movement of the air mass in a much more realistic way, the chance of encountering turbulence and downdrafts is increasing.
The conditions likely to form mountain waves are:
- Wind of at least 15kt flowing perpendicular to the mountain range
- Increase in wind strength with an increase in altitude
- Temperature inversion above the mountain top
Where possible, pilots should avoid areas of known or possible mountain wave activity. If it is necessary to cross a mountain range during these conditions, do so as high above the range as possible, and cross at a 45° angle so that the aircraft can be quickly turned back to the windward side if required.