What Is Marginal Weather?

Hi Readers: Marginal weather is a subject which has bugged pilots for years, and has been the cause of many aircraft accidents - many fatal. Airline pilots, if given marginal weather conditions, automatically expect IFR conditions to follow, and of course they file IFR flight plans anyway. To the GA pilot, marginal weather, depending on the pilot's ratings, experience, and proficiency, is a matter to be dealt with on an individual basis. Too often the GA pilot fools himself by deciding the weather, deteriorating, will get better ahead.
Unless we have divine powers or a degree in meteorology or Aerology, we should not attempt to outguess the weather. Let's let the weather man - briefer, forecaster, or whatever name he goes by, handle the weather for us, X-C or local flight. We should listen closely to his words and ask the routine and difficult questions. As pilots, however, that still does not absolve us of not knowing what VFR, marginal weather, and IFR are and their differences. And the flight, local or X-C, is ours to plan and execute safely.
So marginal weather conditions are somewhere between VFR and IFR - let's get specific.
The FAA defines the term as ceiling 1,000' to 3,000' (AGL), and visibility 3 to 5 miles - interpreted as flight visibility (How expert are we in estimating visibility?). So marginal weather is just beyond VFR and that's usually where the problems start. Unless we are IFR qualified, we should immediately question our ability to continue with our flight plan (if we have one) or alter our course and revise our flight plan. Let's ask ourselves, do we honestly believe, knowing our capabilities, that we should continue the flight.
The National Weather Service, and other weather facilities, stand ready to assist us in our preflight preparations and flight planning, but do not define marginal weather or make decisions with respect to marginal weather. There can be a briefing for the flight, a forecast for the route of flight, or weather advisories. Readily available is METAR, FA (Area forecasts which give MVFR (Marginal VFR) reports for areas of 3,000 Sq miles at any one time, SIGMETS (4 hour period), and AIRMETS (6 hour period). TIBS ( area and route briefings) can be used, but is not considered a substitute for briefings by a weather Specialist (Call 1-800-WX BRIEF). Then there is also AWOS (Automatic Weather Observing System) at most airports, transmitted on a discrete VHF radio frequency - these airports listed in the FAA Airport Facility Directory.
There is a fine line between VFR, MVFR, and IFR conditions due to weather phenomenon such as low-level, layered clouds (associated or not associated with weather fronts) changing ceilings and visibilities with the advent of fog, dust, or haze conditions, even to the point of sky obscuration.
Most aircraft accidents relating to low ceilings and visibilities (flying into marginal weather) are the result of somewhat inactive pilots who are not qualified for IFR flight and, more often than not, attempt flight by visual reference into deteriorating weather conditions. Losing the visual horizon, they are immediately at risk to experience vertigo. If flying by reference to instruments is not accomplished immediately, control of the aircraft may be lost. Continued flight into adverse weather (marginal conditions) is the single cause of the greatest number of fatal accidents.
The best advice is to be aware of, and on the alert for, weather phenomena that may produce marginal VFR and IFR conditions. Above all, pilots should be honest with respect to their capabilities. Can I handle this weather? If not, do a 180 degree turn or change course or altitude immediately - don't wait. Get back to VFR conditions. There will always be another time - perhaps additional proficiency time.
Thanks for listening. R.S.

Aviation Weather Services

Hi Readers: Aviation Weather Services promolgated by the FAA, the NWS, and NASA are best described by and necessarily involve the actual flight, local or x-c, VFR and IFR flight plans; beginning with flight planning, and leading to en route flight, and terminating with descent and approach to land. In addition, the Weather Services provide an assist to the Controllers in preparing for the duties in which they are charged. Even local flights must be considered in terms of current weather - often pilots on local flights are caught in a sudden change of weather from VFR to IFR, as many of the aircraft accidents reveal.
Weather is a 24-hour phenomenom, in constant change of its elements and phases. In 20 minutes a cloud ceiling may ascend or descend 2,000 feet, precipitation can change from rain to ice, and visibilities can become obscured or obliterated.
Since most weather services are tied to a specific phase of flight, let's plan a VFR x-c flight. Without getting into the details, we would either file a flightplan with AFSS/FSS by telephone using TIBS (Telephone Information Briefing Service), a recording of the destination current weather, or talking with a weather specialist concerning the destination current and forecasted weather (1-800-WxBrief- toll free). This is a Preflight Briefing to help the pilot determine a "go" or "no go" decision. Or, if you are computer-oriented, you may file a flight plan with DUATS(Direct User Access Terminal System) - toll free, and get alpha-numeric preflight weather data and file a domestic VFR or IFR flight plan.
We might use, in conjunction with our flight plan or separately, METAR (Aviation routine weather report) or an FA(an area forecast), if advantageous.
After takeoff, we are considered in an en route phase of flight and can utilize several services to our advantage.
Lest we forget, we can still communicate with AFSS/FSS on a common frquency of 122.2 or a discrete frequency for an individual station to file, activate, close, or change a flight plan; request an IFR clearance, contact ATCT/ARTCC for control; file position reports, pass PIREPS (Pilot weather reports); request status of Special Use Airspace; and request assistance in an inflight emergency.
Normally, we might use EFAS (En Route Flight Advisory Service) for nonroutine weather needs in flight or TWEB ( Transcribed Weather Broadcasts) for the routine weather needs in flight. Inflight advisories include SIGMET (Significant Meteorological Information), Convective SIGMETs, AIRMETs (Airmen Meteorological Information), FAs (Area Forecasts) , Winds Aloft Forecasts (176 locations in 48 States), and PIREPs (Reports by pilots of weather conditions in flight).
Descending from en route flight to approach and landing at our destination we might use any number of weather advisories, primarily that concerning the weather at the destination airport or terminal such as FA, LLWAS (Low level wind shear alert system), PIREPs, TAF(Terminal Area Forecast), and WW (Severe Weather Watch). And, of course, our continued communications, depending on VFR or IFR, with ARTCC, TRACON ( Terminal Radar Approach Control), ATCT, and following with GT (Ground Control) to the very end of our flight.
ATCT and TRACON both use air/ground communications, visual signals, and other devices to provide ATC services to aircraft operating in the vicinity of an airport. ATC services authorizes aircraft to land or takeoff at the airport controlled by the tower or to transit the Class D airspace area regardless of flight plan or weather conditions. A tower may also provide approach control services.
To put the aviation weather services in perspective, the pilot must deal with ARTCC, ATCT, and TRACON (as spelled out in AC 00-45F) with respect to their flight plan to effect location and positive control of the aircraft. TRACONs manage the airspace 10 to 400 miles outside of selected airports and below 13,000 feet. They also coordinate spacing as aircraft approach and depart airports. Terminal Controllers are knowlegeable of current weather conditions and are prepared to advise pilots of hazardous weather conditions within a 150 nm sector or area. Tower operators are certified to act as official weather observers.
The December 2007 aircraft Accident Accounting is in process.
Thanks for listening. R.S.