‘VFR Flight Not Recommended….’ How often have you driven instead of flown, only to fume the entire way as you drove through good flying weather?
TEMPTATION: Given the ‘VFR Flight Not Recommended‘ (VFNR) advisory, many pilots would never fly. Others get a few VFNR flights under their belt and decide that this type of flying can be done routinely. Most pilots fall somewhere in between — they agonize over the go/no-go decision, and ‘sometimes’ let non-flying pressures affect their choices. Pilots want to go places and that makes it tempting to fly … regardless of conditions.
RULES: Flight Service is required to give the VFNR advisory when the Area Forecast or any station along your route of flight reports current or forecast visibility below five miles, or cloud ceilings below 3000 feet. If the weather is ‘Marginal VFR‘ (visibility three to five miles or ceilings 1000 to 3000 feet), you can still choose to fly visually when Flight Service advises against it.
Trap: ‘3000 and 5’ is pretty good. ‘1000 and 3’ is not.
DECISION: If you get the VFNR advisory, you should ask…
What conditions (ceiling, visibility or both) caused the advisory?
How bad are the conditions?
Where, and how widespread, are the MVFR conditions? and
When are conditions likely to change — is the trend toward worsening or improving?
STRATEGY: Don’t approach flying in MVFR conditions, without significant planning. Get out a sectional chart and physically draw a line representing your route. Choose significant landmarks (four-lane highways, large power plants, etc.) that will be apparent even in low visibility, from low altitude. Divide your flight into segments between your landmarks and…
*Find airports — always know the direction and distance to the nearest airport.
*Look for obstacles — (terrain and towers) within five miles to either side of your route;
*Pick a minimum safe altitude — above each obstacle and between each landmark; and
*Have an out for each segment — a direction that gives you better clearance;
Important: Decide *on the ground* that you will respond to any reduction in visibility below your comfort level, or below your minimum safe altitude with an escape toward lower obstacles and the nearest airport.
GROUND SPEED AND VISIBILITY: In his book See and Avoid, Dr. Fred G. DeLacerda states that it takes about 12 seconds for a pilot to see and avoid an object — a tenth of a second for the eye to send a signal to the brain; one second to recognize that signal as an object; five seconds to decide if there’s a collision potential; four seconds to decide on an evasive maneuver; four-tenths of a second to command the body to make control inputs, and up to two seconds for the airplane to respond.
Translation: At 90kts across the ground, you’ll go 0.3 miles from the time you see an object to the earliest moment you can expect to begin a change in flight path. At 120kts, you’ll fly 0.4 miles, and at 150kts you’ll cover half a mile. There are lots of things to keep track of, so don’t assume you’ll see an obstacle right away.
POSITION: Closely follow your progress along the line you drew on the chart — even the best GPS moving maps sometimes quit, and many don’t give any terrain or obstacle information.
ESCAPE: At 90kts groundspeed, your 180-degree-standard-turn diameter is one mile. At 120kts, the escape path will be 1.3 miles offset from your entry, and at 150kts, the way out is 1.6 miles away from the way you took in.
Translation: In low visibility you may not be able to see what you’re turning into until you’re committed to the turn and, if you’ve been flying slow, you’d better keep it shallow.
THE BOTTOM LINE At four miles visibility and 120kts you can only see two minutes into your future. You need to know obstructions, headings, routes, landmarks, and ETAs, and be able to collect that information without wasting time with your eyes in the cockpit. VFNR is an exercise in options and survival — lose your options, and you may lose your life.
Editor’s Note:This article originally ran when iPilot was just a baby. Be sure to check the Insider Series Archive for more great stories you may have missed.