Content

Meteorological conditions significantly impact on flight safety and aircraft performance. When flying visually, you must adhere to certain minimum visibility criteria, which includes maintaining a minimum distance from cloud in order to ensure safe separation from both terrain and other traffic. When you are done with this presentation, you should be able to:

• Understand that the different regulations is depending on the weather situation.
• Explain the weather minima in different airspaces regarding visibility and distance to clouds.
• Explain the reason and conditions for special VFR.
• Describe planning minima and when it is applicable.

This presentation will take approximately 30 minutes to complete.

Regulations

Accurate assessment of weather conditions presents a significant challenge to the pilot, and if judged poorly can threaten the safety of the flight as well as the legality. Weather conditions are generally separated in to two environments:

• VMC - Visual Meteorological Conditions
• IMC - Instrument Meteorological Conditions

These two conditions can be broadly considered as good or bad flight environments. When VMC prevails, you will generally have sufficient visual references to detect and avoid collision with both the terrain and other traffic. Meteorological requirements, including visibility, will generally vary depending on altitude and airspace classification. If you are unable to maintain these minima, you are considered to be flying IMC, which means you have either reduced visibility or no visibility at all, and therefore flight in this environment requires navigation using the airplane instruments

The two flight conditions conform to two sets of flight rules:

• VFR - Visual Flight Rules
• IFR - Instrument Flight Rules

This training only qualifies you to fly VFR, which means you have to stay in VMC at all times. If you fly IFR, on the other hand, you can fly in both IMC and VMC, which means you can fly in almost all conditions. Flying IFR requires an IR (Instrument Rating), which is available in different categories. This rating requires both experience in the form of flight time and further training.

Controlled airspace

VMC minima varies depending on airspace, and in Sweden there are generally only two classes of airspace - controlled (C) and uncontrolled (G). In controlled airspace, the visibility must be at least 5 km and you must maintain a distance from cloud of at least 1000 feet vertically and 1500 metres horizontally, with two exceptions:

• At or above 10 000 feet MSL, visibility must be at least 8 km with distance from cloud still 1000 feet vertically and 1500 metres horizontally.
• In a control zone you can request special VFR, which means you must fly below 140 knots, be free of cloud and have a visibility of at least 1.5 km.

Unless you have received special VFR, you may not take off or land at an airport within a control zone if the visibility is less than 5 km and the cloud ceiling is below 1500 feet.

The basic rule states that you must meet a minimum requirement of 5 km in order to navigate and avoid terrain. In addition, since there may be IFR traffic, you need to keep a distance from cloud of at least 1000 feet vertically and 1500 metres horizontally. This gives you enough time to detect and avoid a collision with any traffic appearing through a cloud.

When flying at or above 10 000 feet MSL, the distance from ground becomes so great it can become difficult to discern ground terrain features, therefore you must have better visibility in order to navigate. Note that the altitudes quoted in the regulation are referenced to mean sea level (MSL). You also need to keep the same distance from cloud at this altitude as the others, in order to avoid collision with other traffic.

A control zone is a controlled airspace that extends from a certain altitude all the way down to the ground or water and is monitored by an air traffic control tower. To make it easier for aircraft to take off and land at a controlled airport, you can request special VFR, which means that the controller assumes responsibility for the separation between aircraft. To facilitate this, it usually means that the controller only allows one aircraft into the control zone at a time, and you are still responsible for clearance between ground obstacles and the terrain. Because an air traffic controller separates you from other traffic, you can fly free from cloud with a flight visibility down to 1.5 km, as long as you keep the surface in sight, maintain a speed below 140 knots and make speed adjustments accordingly. An air traffic controller shall not permit aircraft to take off, land or even enter the control zone if the ground visibility is less than 1.5 km or the cloud ceiling height is below 600 feet.

The reason you are not allowed to take-off or land in a control zone when the visibility is less than 5 km, or the cloud ceiling height is below 1500 feet, is because it is below the VMC minima. These minima ensure you have a vertical distance from cloud of at least 1000 feet, while the lowest altitude you can fly at is 500 feet. Cloud ceiling means the height above the ground or water of the base of the lowest layer of cloud below 20 000 feet covering more than half the sky.

Uncontrolled airspace

Even in uncontrolled airspace, the flight visibility should be at least 5 km and you should maintain a distance from cloud of at least 1000 feet vertically and 1500 metres horizontally, with one exception:

• At or below the higher of 3000 feet MSL or 1000 feet AGL, you are only required to be free of cloud. Visibility must still be at least 5 km, except under two circumstances:
  • During flight below 140 knots, where a comfortable safety margin in order to detect obstacles and other traffic exists, the visibility can be reduced to 3 km.
  • During flight under 140 knots in the traffic circuit with the airport in sight, the visibility can be reduced to 1.5 km.

As is the case with controlled airspace, the basic rule states that you must meet a minimum requirement of 5 km visibility in order to navigate and avoid terrain. In addition, you must keep a distance from cloud of at least 1000 feet vertically and 1500 metres horizontally to avoid other traffic.

The exception applies at lower altitudes in uncontrolled airspace since there should be no IFR traffic there. Here you are only required to remain free from cloud, which means there is no separation minima to clouds to comply with. However, you must not fly through cloud formations as this would clearly reduce visibility below permitted values. At or below the higher of 3000 feet MSL or 1000 feet AGL, means that you will always have some altitude margin when flying using these rule exceptions, even if the terrain becomes higher, since 1000 feet AGL is referenced to above ground level (AGL). If you fly below 140 knots and adjust the speed to detect other traffic or obstacles, you can reduce the visibility requirement further to 3 km.

When flying in the traffic circuit with the runway in sight, you can reduce the visibility requirement to 1.5 km. You are still expected to adjust the speed and fly below 140 knots while flying free from cloud.

It should be noted that flight visibility, as quoted in the different airspace minima, is considered the visibility forward of the cockpit, essentially what the pilots would see.

planning minima

Before a flight with an ultralight aircraft you have to prepare. If you are flying more than 5 nautical miles from the departure airport or leaving the control zone the airport is located in, you must review the weather for the flight and plan for any action if the flight cannot be completed due to the weather.

There is also something called a planning minima. You may not begin a distance flight if the visibility is lower than 5 km or the cloud ceiling height is lower than 1000 feet. A distance flight is a flight that exceeds 25 nautical miles from the departure airport. This weather must be met both at the departure airport, the destination and en-route while you are flying. If you are only flying a local flight, however, you only need to take into account the operational regulations for a visual flight. If the weather is less than 8 km or 2000 feet for a distance flight, the weather must be documented and taken onboard. This basically means that you can bring notes or a screenshot on your cellphone.