Q: What’s the deadliest category of general aviation accidents?
A: Attempted visual flight into Instrument Meteorological Conditions (IMC). According to AOPA’s Air Safety Institute, when a “VFR into IMC” crash occurs, it is almost always fatal.
Q: Who’s at risk of a Visual Flight Rules (VFR) flight into IMC?
A: Experienced, often high-time pilots, in cross-country (not training-type) airplanes are as much at risk as lower-time pilots. AOPA’s Richard McSpadden writes, “a third of these accidents [VFR into IMC] happen to experienced, IFR-rated pilots.”
Q: When are you most likely to inadvertently enter instrument conditions?
A: When beginning or continuing a flight into marginal weather conditions.
There is no official definition of scud running. Yet a picture likely pops into your mind. You may envision flight low across the terrain, tendrils of rainy cloud reaching from a low overcast to meet the fog below. You may think of a solid yet rainless overcast, a few hundred to a thousand feet or so above the ground, a bright ribbon of light on the horizon promising clear skies ahead. You might picture a sunny summer day, steamy and hot, so bright with haze that you can’t see more than a mile ahead. Or you might consider flight on a dark night, the stars and moon hidden by clouds, the lights below you occasionally flickering and disappearing behind wisps of condensation. Visual-rules flight in any of these conditions is sometimes called “scud-running.”
Scud running implies an intentionally hazardous flirtation with visual flight in near (or actual) IMC. Under some conditions, flight under a fairly low cloud deck or at fairly low visibilities can be done safely. In the context of this discussion, I’ll refer to managing the risks of legal visual-rules flight in marginal VFR (MVFR) conditions. Few pilots routinely fly VFR in this kind of weather, but sometimes it makes sense for short repositioning flights or other reasons. We need to consider technique and go/no-go decision-making when faced with these conditions.
When MVFR Turns Worse
For the years 2005 to 2014, AOPA’s Air Safety Institute notes 290 NTSB-reported accidents involving attempted or continued visual flight into IMC. That’s about one every other week, with 85 percent of these accidents fatal. Almost two-thirds involve high-performance airplanes, flown typically by experienced pilots who are often instrument rated but chose for whatever reason to fly VFR in marginal conditions. VFR into IMC accidents in high-performance airplanes are over 90 percent fatal.
These types of accidents are avoidable with prudent pilot decision-making. With awareness of the MVFR threat even to experienced pilots, we can derive some recommendations for operation in and around marginal weather conditions and apply knowledge of the conditions that lead to MVFR and IMC to manage the risks and remain in command of your flight.
Risk Management and Mitigation
In an overwhelming number of these accidents, less-than-VFR conditions were reported well before the crash. We’re living in an age where weather data is widely available before and even during flight – all we have to do is look. Check at least once an hour on long trips. Jot down notes to see if the weather trend is improving or deteriorating next time you look, and to verify or refute the accuracy of the forecasts you heard before takeoff. If you’re told St. Louis is expected to be clear all morning, for example, only to find its 2,000 broken when you actually fly over, you know to suspect the forecast of VFR for your destination farther down the road.
“SVFR [Special VFR] allows for graduated risk in decision making. If CAVU represents the least risk, IFR in VMC is perhaps a little less, IFR in IMC a little more, and SVFR is a little more than that.” – Paul Bertorelli
Let’s say marginal weather conditions exist for a portion of your flight, your route is entirely away from mountains, and you’ll easily complete your trip during daylight hours. How can you minimize risks and avoid becoming a scud-running statistic?
1. Know what MVFR looks like.
Most flight instruction takes place in excellent weather. Even instrument training is usually conducted in good Visual Meteorological Conditions (VMC). When weather is marginal, instrument pilot training is usually done on instrument routes and instrument flight plans. That makes sense, given the IFR training mission. No wonder then that the MVFR accident record is abysmal. Almost no one trains for it before actually trying it alone.
The next time the cloud ceiling hovers around 1,500 feet, or the visibility is about five miles (preferably not both the first time), hire an instructor for a short round-robin training flight under Visual Flight Rules (VFR), including landing on at least one airport other than your home base. Your instructor should be extremely familiar with the local area’s obstructions and navigation features, as well as your make and model of airplane. He or she will serve as an extra set of hands and eyes in the cockpit should you need any help.
Even your home airport will look different from low altitude or in marginal weather; you’ll be amazed at the increase in workload and anxiety brought on by a loss of normal visual cues and gain a healthy respect for the risks of MVFR flight. I bet if you knew ahead of time you were going to fly this exercise that you would spend a lot of time looking at the charts and pinpointing obstacles, finding landmarks you can use along the way, and thinking about how you would find the airport and enter its pattern. This is the way you should always approach flight at altitudes or in visibility less than normal for you.
2. Know where you’re going.
Safe flight in marginal conditions demands thorough preflight planning. You need to determine what route you’ll use, and where you’ll go if your primary route is closed off by weather.
GPS is a wonderful thing. The proliferation of moving map displays and apps greatly increases a pilot’s orientation. In the context of low-altitude, low-visibility flight, however, GPS may be more limited than you’d think. Some models have minimum safe altitude or minimum en route altitude information, but they use the standard FAA criteria of 1,000 feet above terrain (2,000 feet in mountainous areas), which may be higher than you’re flying in marginal conditions. Unless you keep your GPS database updated, it may not warn of new obstacles along your route. To safely fly MVFR, you need to combine information from GPS and sectional charts (paper or electronic) and plan your route over and around terrain and obstructions. Follow highways and other prominent landmarks to crosscheck the moving map. Keeping to the right of roads, you’ll be better able to see your landmark out the left side of the airplane (and you’ll avoid the other MVFR pilot coming from the opposite direction). Fly from airport to airport, making a new go/no-go decision each time you pass another runway. Review landmarks near your destination so you can find it in the murk. Even with GPS it may not be as easy to find as you think.
3. Define and fly minimum altitudes.
Plot the minimum safe altitude for each segment of your planned flight. At a bare minimum 14 CFR 91.199 (or equivalent in non-U.S. airspace) applies: for fixed-wing aircraft, at least 500 feet above the ground, obstacle or individual at any point except over open water or sparsely populated areas, and at least 1000 feet above the highest obstacle within 2000 feet laterally over congested areas. Helicopters may fly lower, provided the pilot complies with FAA-prescribed routes and altitudes. Crosscheck these altitudes against the VFR visibility and cloud clearance requirements of the airspace in which you’ll fly, and you can derive specific minimum (and perhaps maximum) altitudes for each segment of your flight. Chances are you’ll have a series of altitudes that changes as you progress toward your planned destination.
4. Slow down.
There may be a reason retractable gear and multi-engine airplanes are involved in more scud-running accidents than their proportion in the general aviation fleet. The faster you’re flying, the harder it’s going to be to avoid obstacles in low-visibility flight.
In his collision-avoidance book, “See and Avoid,” Fred Delacerda quantifies the process of detecting and avoiding obstacles: “It takes the average human about 10 seconds to visually acquire a conflict, recognize it as a threat, decide to take evasive action, and make a control movement to avoid the obstacle. It takes the airplane, on average, one to two more seconds to respond to the pilot’s command.” In the average 12 seconds it takes, then, to detect and maneuver around an object, an airplane flying at 90 knots ground speed covers 0.3 miles. Cruising at 120 knots, you’ll fly 0.4 miles in that time. If you’re flying 150 knots across the ground, you’ll cover half a mile. At 180 knots ground speed, you’ll fly 0.6 miles in this decision-making time. That doesn’t leave a lot of room for error when trying to avoid hard-to-see towers or hills in low visibility.
Slow down! Practice power settings and configurations that allow you to cruise at slower-than-normal speeds while still maintaining a healthy margin above a stall. Use the configuration you use for downwind in the traffic pattern, maybe even gear down in retractable gear airplanes. The slower you’re flying, the better able you’ll be to see and avoid a threat.
5. Use your autopilot.
I’m in favor of hand-flying the airplane as much as possible, but MVFR flight is a time when a good autopilot is one of your best tools. Let the machine fly itself, with close monitoring by you. As pilot monitoring the autopilot, you have more bandwidth to address the MVFR functions of navigation and obstacle avoidance.
6. Plan your escape.
Like any other go/no-go decision, MVFR flight requires you always leave yourself a way out. Because of the time you’ve put into planning your MVFR flight, you now have specific criteria to meet at all times: a minimum altitude, perhaps a maximum altitude for cloud clearance or airspace, and a minimum visibility. If at any time it appears you may soon violate any one of these criteria, execute your escape at once. Do not wait to decide. It will not get better a little further along.
The classic fix for flying into worsening weather is a 180-degree turn back from where you came – a good idea if conditions worsen, or you start to feel uncomfortable with your original plan. Here, too, you’ll find a big safety advantage in slowing down and using your autopilot if you have one.
In zero wind and at 120 knots ground speed, the diameter of a 180-degree turn (assuming 3 degrees per second, or a standard rate) is about 1.3 miles. One hundred fifty knots yields 1.6 miles off your entry track, and 180 knots puts you nearly two miles off the safe path you used to enter. You may elect to use steeper banks, but they present their own hazards in MVFR. Regardless, in many cases, you won’t be able to see obstacles on your escape route until you’re well established in your turn.
Another escape path is to go up. If visibility is poor but skies are clear, there’s little hazard in climbing. You’ll be in a better position to navigate by radio and to call someone for help at a higher altitude. If you’re flying under a ceiling, climbing VFR through the clouds is absolutely a last-chance technique. But it’s an option if you need it, as long as you’ve got the training, recent experience and equipment to maintain control by reference to instruments. From there, it’s time to confess your sins to Air Traffic Control and get help to reach the ground. Worry about possible consequences later.
7. Know your limitations.
AOPA tells us pilots without instrument training typically lose control of the airplane about 180 seconds after entering IMC. That’s three minutes to live. If you wait 30 seconds after entering IMC before beginning an escape, you may lose control less than a minute after rolling out on the reverse course, maybe sooner, if you’re a VFR pilot.
If you’re a rusty instrument pilot, or you’re flying an airplane not equipped the way you usually fly in the clouds (an airline pilot flying a general aviation airplane, for instance), you may have a better chance to maintain control, but you’re still not immune. This is definitely not a situation to convince yourself that you’re better than you really are, or to put off practice until you’re in the game for real. Again, if you have an autopilot, your escape is the time to use it.
Making the Decision
It’s not the weather itself that causes accidents. It’s the way we make decisions about flying in weather. Approach MVFR flight with all the preparation and forethought you’d use on an instrument trip. Do whatever you can to reduce your inflight workload. Fly as slowly as you safely can to have more time to see and avoid obstacles. Know your minimum and maximum altitudes at each point along the way, and the minimum visibility, and use your escape route without hesitation if it appears you may have to violate one or more of those criteria if you continue.