Aviation Weather
and Performance
Cloud ceilings and visibility minima, ILS categories, the International Standard Atmosphere, icing types and holdover, de-icing decisions, hurricane season, the South China Sea deviations and the special-approach airports that need simulator training.
Reviewed by Kevin Singh, Founder · Fact-checked against Icarus Jet fleet and airport operations data · Last updated 10 September 2026
The working reference
How weather and performance work for a private flight
Weather decides whether a private flight goes, where it lands and how much it carries. A ceiling is the lowest broken or overcast layer; few and scattered layers do not count, and no broken or overcast layer in the METAR or TAF means an unlimited ceiling. Basic VFR needs three statute miles and the cloud clearances; a CAT I ILS needs about 1,800 feet of visibility and a 200 foot decision altitude, CAT II about 1,200 feet and 100 feet, and CAT III lands with a decision height of 50 feet or lower. The International Standard Atmosphere sets sea level at 1013.25 hectopascals and 15 degrees, losing about two degrees per thousand feet, and every performance chart is corrected from it, which is why a hot day at a high field shortens the runway. Icing forms in visible moisture between about freezing and minus 40, as clear ice, rime, mixed or frost; de-icing removes it with heated fluid and anti-icing buys a holdover of roughly 20 to 40 minutes, decided by the captain and billed after the event. Hurricane season runs 1 June to 30 November and peaks from mid-August to mid-October; large-scale weather deviations over the South China Sea run June to October and hold business jets below FL400 with thirty extra minutes of fuel. London City, Chambéry, Annecy, Innsbruck and Madeira need simulator training for the approach. The desk briefs the ceiling and visibility against the aircraft's minima, plans the alternate and the fuel, and books the de-icing before the crew needs it.
Ceilings and visibility
The ceiling is the lowest layer reported broken (five to seven eighths) or overcast; few and scattered do not form one. Rules of thumb: about 200 feet for a non-precision approach and about 100 feet for an ILS. Visibility for landing: three statute miles VFR, about 1,800 feet RVR for CAT I with a 200 foot decision altitude, about 1,200 feet for CAT II at 100 feet, and CAT III at 50 feet or lower.
The standard atmosphere
ISA sea level is 1013.25 hectopascals and 15 degrees Celsius, with a lapse rate of 6.5 degrees per kilometre, about 1.98 degrees per thousand feet. ISA temperature at altitude is 15 minus the lapse rate times the height. Performance charts are corrected from ISA, so a hot day at a high field costs runway and payload.
Icing
Icing needs visible moisture and temperatures roughly between freezing and minus 40. Clear ice from large supercooled droplets is transparent and hard to see; rime from small droplets is opaque and rough; mixed ice and frost complete the set. Structural icing is the most common kind, and the article on icing types carries the recognition cues.
De-icing and anti-icing
De-icing removes contamination with heated fluid; anti-icing applies a second fluid that buys a holdover of roughly 20 to 40 minutes depending on the fluid type and the conditions. The pilot in command decides, the availability of fluid and equipment is checked before departure, and de-icing sits outside the charter contract and is billed after the event.
Seasons that shape routings
Hurricane season, 1 June to 30 November, peaking mid-August to mid-October across the Caribbean and Florida, with the aircraft moved ahead of the storm. South China Sea large-scale weather deviations from June to October: flight level allocation by airway, business jets below FL400, flow control and thirty extra minutes of fuel. Canadian winter operations and Aspen's drained water systems on the Americas pages.
Special approaches
London City, Chambéry, Annecy and Innsbruck require simulator training for the captain and first officer; Madeira requires it for the captain plus CAA approval; Cannes, Sion, Lugano and Samedan require computer-based training. Short-runway alternates run from about 5,000 to 6,000 feet, so the aircraft and the weather are matched to the field before the trip is quoted.
Where it applies
How the rule changes by region
Caribbean and the US East Coast
Hurricane season from June to November with the mid-August to mid-October peak, the storm watch, the reposition ahead of the track and the alternates outside it.
Asia
South China Sea large-scale weather deviations from June to October, with Singapore Changi and Tokyo Haneda as the diversion fields of choice and handling booked ahead.
Europe and the Alps
The special-approach airports that need simulator or computer-based training, winter de-icing across the north, the summer thunderstorm slot regulations in the south.
Americas
Canadian winter operations for US crews, Aspen and the mountain fields with drained water systems and density altitude, the Florida summer convection.
Middle East and Africa
Heat and density altitude on the summer departures, sand and haboobs on the Gulf ramps, the equatorial convection on the African crossings.
The oceans
North Atlantic weather deviation on the special procedures, Pacific routings sized around the diversion arcs, ETOPS on the slots and ATC page.
Guides and updates
Weather articles from the desk
The detailed pieces behind this page, newest first, each with the year it was written and the discipline it belongs to.
How Much Visibility Is Needed to Land a Plane?
Explains VFR, IFR and ILS CAT I/II/III visibility and decision-height minima in lay terms.
Read the guide2023Weather and performanceUnderstanding the Various Aviation Icing Types
A long explainer on aircraft icing conditions, the clear/rime/mixed/frost types, their effect on performance and the de-icing fluid types.
Read the guide2023Weather and performanceWhat is a Cloud Ceiling and How Does it Impact Aviation?
Explains what a cloud ceiling is versus cloud base, how to read it from METAR/TAF cloud codes, and why it drives VFR/IFR and approach decisions.
Read the guide2023Weather and performanceGuide to International Standard Atmosphere
Explains the ISA model, its sea-level constants and lapse rate, how to compute ISA temperature at altitude, and how it differs from the US Standard Atmosphere.
Read the guide2023Weather and performanceIn Plane Sight: Understanding the Critical Role of Visibility in Safe Aircraft Landings
Explainer on visibility, VFR vs ILS, low-visibility procedures and ICAO/FAA rules, with a list of European airports that require special crew training for non-scheduled operations.
Read the guide2019Weather and performanceDe-Icing and Anti-Icing of a Private Jet
Explains the difference between de-icing and anti-icing, why the cost is excluded from charter quotes, and typical US prices by aircraft size.
Read the guideCountry guides
Where the rule differs by country
The regional pages that carry the detail for this discipline, each with the permit, entry, slot, handling and fuel facts for that country.
Questions
Aviation weather questions
What is a cloud ceiling?
The height of the lowest layer reported broken, five to seven eighths, or overcast. Few and scattered layers do not form a ceiling, and no broken or overcast layer in the METAR or TAF means the ceiling is unlimited.
How much visibility does a plane need to land?
Three statute miles under basic VFR. On an ILS, about 1,800 feet of runway visual range for CAT I with a 200 foot decision altitude, about 1,200 feet for CAT II at 100 feet, and a decision height of 50 feet or lower for CAT III.
What is the International Standard Atmosphere?
The reference atmosphere every performance chart is built on: 1013.25 hectopascals and 15 degrees Celsius at sea level, falling about 1.98 degrees per thousand feet. The difference between the day and ISA is what corrects the runway and climb figures.
What are the types of aircraft icing?
Clear ice from large supercooled droplets, transparent and hard to see; rime ice from small droplets, opaque and rough; mixed ice; and frost. Icing needs visible moisture and temperatures roughly between freezing and minus 40, and structural icing is the most common kind.
What is the difference between de-icing and anti-icing?
De-icing removes snow, ice and frost with heated fluid. Anti-icing applies a second fluid that stops new contamination forming for a holdover of roughly 20 to 40 minutes. The captain decides, and the fluid and the truck are confirmed before the crew needs them.
Who pays for de-icing on a charter flight?
The client, after the event, because de-icing sits outside the charter contract and is billed against the card on file when it is used. The cost depends on the aircraft size and the fluid used, and the desk quotes the range before the trip.
When is hurricane season?
From 1 June to 30 November, peaking from mid-August to mid-October across the Caribbean and Florida. The desk watches the forecasts, moves the aircraft ahead of a storm and holds alternates outside its path.
What is a large-scale weather deviation?
A procedure over the South China Sea roughly June to October that assigns flight levels by airway, holds business jets below FL400 and adds flow control and crossing-time restrictions. The desk carries thirty extra minutes of fuel and books Singapore or Tokyo as the diversion.
Which airports need special training to fly into?
London City, Chambéry, Annecy and Innsbruck need simulator training for both pilots; Madeira needs it for the captain with CAA approval; Cannes, Sion, Lugano and Samedan need computer-based training. The desk matches the crew and the aircraft to the field before quoting.
What does the desk brief before a weather-critical flight?
The ceiling and visibility against the aircraft's minima, the icing picture and the de-icing plan, the alternates and the fuel to reach them, the storm track in season, and the performance at the departure and arrival fields corrected from ISA.
Get it filed
Weather briefed, alternates held
Send the schedule and the aircraft, and the desk briefs the ceiling, visibility and icing against the minima, holds the alternates and the fuel, and books the de-icing before the crew needs it.
Contact UsPrefer to talk? Call +1 888 277 7203 or email tripsupport@icarusjet.com. The desk is staffed 24/7.