פורסם עם: האם תכננת "נתיב מוצא" ???
המסמך המקורי
Private pilot
CFI Flying on Top-
Legal and Smart?
BY LEROY COOK
Leroy Cook is a Midwest based flight school owner, instructor and aviation enthusiast.
He’s a Gold Seal flight instructor with single- and multi-engine airplane, instrument and glider ratings , an ATP with single and multi-engine airplane ratings , and a commercial pilot with glider and single-engine sea ratings. His first CFI(Certified flight instructor) column was published in the December 1971 issue of PRIVATE PILOT. He’s still a student pilot who learns from his students daily. You can e-mail cook at leroycook@osagevalley.net.
IT’S DECISION TIME. You’re cruising through increasingly hazy skies when puffy coagulations of water vapor begin to appear, just about at your flight level. Clouds were not in your plans when you picked this altitude, nor had you bothered to check the forecast. Do you drop down to stay solidly underneath the clouds or climb to stay 1000 feet above the tops at a VFR altitude? Or do you attempt a hurried airfile of an IFR flight plan, hoping your rusty IFR skills are equal to whatever lies ahead?
Experience and ratings aside, every flight involving restrictins to visibility poses its own set of problems. Making decisions, like how best to dill with a cloud deck, is what piloting is all about. If you’re poorly prepared for what has become a clouded situation, you’ll want to gather some information about conditions along the route.
Perhaps you’ve been dialing up ATIS or AWOS frequencies to get a feel for reported cloud heights ahead. Now a call to FSS or, even better, Flight Watch on 122.0 if you have sufficient altitude, would be in order, to make sure you can handle the unseen weather farther down the road. Luckily , you learn that the weather ahead is relatively benign. The clouds aren’t going to spawn storms or push down to the ground level. Nevertheless, you can’t stay at your current altitude, so which way do you move? As a student pilot, you were thaught to always remain in full contact with the ground, as required by FAR 61.89 (a) (7). This doesn’t mean students can not fly above a few scattered, inconsequential puffballs, but they must be able to navigate by pioltage and should descend immediately if the clouds show any tendency to reach 50% coverage. For the rest of us, flight on top of a solid cloud deck is legal, as long as we observe the rules. Whether or not it is smart depends on our qualifications and our respect for the limitations they impose. Even if you have an instrument rating, you may be unable to file instruments because you or the airplane lack currency. If your airplane or your license is limited to VFR operations, or you can’t speak with FSS or ATC in your area, you must play the game with the cards you have. You can’t bet on another draw. In these cases, go on top only if you have a gilt-edged guarantee that you can descend in VFR conditions at the end of your flight.
Broken (5/8 to 7/8 coverage) can become overcast quickly, and if you don’t have holes at least a mile in diameter, allowing you to circle 2000 feet away from clouds as you descend, you can’t drop down under VFR.
A scattered (4/8 or less) undercast is not an immediate hazard for a VFR pilot, although puffy clouds hiding pilotage landmarks can cause navigational difficulties. You better have a couple of backup navigation methods on tap, just to keep running tabs on your position. Don’t ignore the formation of scattered puffs beneath a rainy overcast, which can presage a low stratus layer forming as the air at ground level becomes saturated. Turn around or scudrun to the nearest airport if it increases. Remember, cloud heights reported in the broadcast weather observations are in height above ground level. So a 1500-foot cloud layer on the ATIS will have its bases at 1500 feet plus the terrain elevation at the reporting point. And tops will be far above that- usually 1000 feet higher than you planned. You can ask Flight Watch for any tops reports they have received, but pay attention to the time of observation; conditions change as heating , terrain lifting or saturation occur. So a two-hour-old PIREP won’t do you much good.
Going Up
What’s your legal VFR-on-top cruising altitude? As the FARs require , it’s an altitude at least 1000 feet above any cloud, then adjusted to comply with the hemispherical rule. So tops at 4300 feet msl require a climb to 5500 feet for an eastbound plane, unless you can note terrain elevations of 2500 feet or more. In that case the hemisphere rule wont take effect until 5500 feet, leaving you free to cruise at whatever altitude you like below that. However, it’s a good idea to observe the odd/even-plus-500 rule even below 3000 feet agl. In all cases, however, you must remain 1000 feet above the tops.
If you file IFR and ask for VFR- on-top as your cruising altitude, you take on added responsibilities. You must be 1000 feet or more above the clouds, be at the correct VFR altitude for your
On-top VFR flight is a beautiful option, but it has to be handled correctly.
Direction of flight and report any change in altitude to ATC, which is basing separation from other IFR traffic on knowing your level-flight altitude. Meanwhile, you have to assume responsibility for avoiding any VFR traffic that might come along.
Now What?
O.K. You’ve flown VFR over the top of a thickening cloud layer, passed up several areas with good holes and now you realize that you aren’t going to have any openings at your destination.
The solid-white expanse underneath looks foreboding, and you wonder what’s below it. Unless you can legally negotiate for a clearance to descend under IFR, or you feel the pressing need to declare an emergency so ATC can clear a path for a VFR pilot coming down through the soup, your best bet is to make a 180 back to the direction from whence you came. That’s where holes were present and where they hopefully still exist. Ask flight service where the clouds are broken or better, and take this action before you run low on fuel and limit your options.
Have you practiced a tight, descending spiral for use under these conditions? Most unprepared pilots will spot a cloud opening, start a dive for the hole and sail past it as the airspeed goes into the yellow arc. This prompts them to turn around at warp speed, probably, steepening the bank as they enter the canyon of cloud. And they’ll all too often drop out the turbulent bottom in a less-than-controlled twisting dive. Even if the airplane survives this stressful encounter, it takes a lot of space to getthe aircraft turned around and down.
The better techniqe is to slow to an airspeed beneath the maximum flap speed, extend the flaps and landing gear if available, trim to hold the speed at a safe value above stall while banked at 30 to 40 degrees, and make a low power decent in a tight, controlled circle. This requires only a quarter-mile column of clear air and keeps the aircraft at a low G loading. Bring the power back up, and clean up the airplane to level off. Bear in mind that you’ll need to resume your on-course heading when you level out 500 feet below the clouds. Now that you’re down low, start watching for terrain and tower hazards.
What about the risk of engine failure while flying over an undercast in a single-engine airplane or a twin operated above its effective single-engine ceiling? This is another case of risk that requires management. You need to know what’s under those clouds to decide if you can survive an engine failure on top. Does the terrain masked by the undercast offer a chance of landing without injury? Is there enough space between cloud base and ground to allow maneuvering for the forced landing, and is the visibility adequate to select a field? As with descent option at the end of the flight, a VFR pilot (or an IFR one, for that matter) needs to keep track of the conditions underneath.
There are times when the serenity of VFR on-top flight is vastly preferable to the hot , bumpy, low –visibility flying underneath. Towers and ridgelines can loom up quickly at 120mph, and the demands of precise navigation increase when checkpoints are only visible less then 5 miles away. Bear in mind that one still has to navigate while on top, often relying heavily on electronic guidance from VOR courses or a lim-dandy GPS screen. As with any navigation method, one should back up the electronic boxes with secondary crosschecks from independent systems and with dead reckoning. If you don’t have this available, stay over broken clouds that offer pilotage peeks.
On-top VFR flight is a beautiful option, but it has to be handled correctly. Don’t proceed blindly and let yourself run out of options. 