AOPA Pilot Magazine
October 2001 Volume 44 / Number 10
Ounce of Prevention Part 10 of 12: Shades of Gray
VFR-into-IMC's slippery slope
We had a window. After staging a successful photo mission from the Manitowoc (Wisconsin) Airport over the weekend, we needed to reposition a Beech A36 Bonanza to another field about 40 nm away. A serious thunderstorm was grumbling toward central Wisconsin; the briefer estimated one and one-half hours before it would masticate the skies over our intended destination.
We had two instrument-rated pilots on board, a UPS Aviation Technologies Apollo MX20 moving map linked to an Apollo GX60 approach-capable GPS, weather radar, and a Goodrich Stormscope. Our preference was to fly VFR, maintaining visual separation from the nastiness ahead. En route, visibilities were called as five to six miles in haze, with ragged, broken to scattered clouds at 4,000 feet — the scud ahead of the storm.
We did not have six miles' visibility, that's for sure. With the sun at our backs, our view forward was still VFR, but not an inch more. I asked my copilot to act as safety pilot and look for traffic so I could stay on the gauges. With the MX20 lighting the way — and the strikes so powerful beyond our destination that they lit up along our course line — we made it to touchdown 15 minutes before the first bolt hit the field.
The number-one cause of weather-related accidents is continued VFR flight into instrument meteorological conditions (IMC). A full quarter of these pilots are instrument-rated. The rate and severity of accidents classified as VFR-into-IMC haven't changed much since the mid-1970s, nor have the causal factors, according to a study by the University of Illinois published earlier this year. The aviation community hasn't had much success discouraging pilots from flying into weather for which they are neither equipped nor prepared. The distinguishing hallmark of a VFR-into-IMC accident is its devastating hand. Roughly 75 percent of these accidents are fatal, because they typically involve a loss of control that starts relatively soon after the airplane enters the clouds.
During our flight, we were flying in classic marginal VFR conditions — the kind that can go sour at any point. We continued on with two thoughts in mind: We could turn around to good VFR at any time, and we could file IFR if it looked like the view ahead was IMC and we wanted to press on. Constantly we assessed the situation. Still, the lure of pressing on VFR grew stronger the closer that we got to our destination. Comforted by the glow of the MX20 — in stark contrast to the view outside — it was clear how enticing those last miles seemed.
There are times when VFR flight is legal but not necessarily safe. In most airspace, three miles and a 1,000-foot ceiling constitute VFR conditions. However, in area forecasts, visibilities of three to five miles are referred to as marginal VFR. Perhaps this is the better definition, because the implication is instant: marginal. On the edge. Not cut-and-dried VFR. But the gradual transition from VFR to IFR conditions often encountered when marginal VFR is forecast can make it difficult to determine when the line is crossed.
Failure to diagnose this change properly can lead pilots to continue flight into adverse weather. All things considered, if pilots know the weather is deteriorating to IFR, they will not fly into it, according to the University of Illinois study.
Pilots who become involved in these fatal weather encounters don't fit neatly into one profile, but they tend to be lower-time pilots than those involved in other types of general aviation accidents; and they are private pilots, as opposed to having more advanced certificates (71.6 percent of those pilots involved in 409 accidents surveyed by the study noted above had private pilot certificates or less).
We are taught that we can manage the risks associated with flying; otherwise few of us would get into an airplane. Those with low time and little experience flying in adverse weather may underestimate the risks associated with flying in marginal conditions. Since we are preached confidence in our abilities, the mix can be deadly.
A cross section of the weather
If we know what's out there, we can avoid stumbling into conditions beyond our ken. To this end, we need to learn as much about the weather before and during a flight as we reasonably can.
The preflight visit to a flight service station briefer who chats with you over coffee is all but history. Though we can wax nostalgic about a personal touch, that's no longer an option for most of us. In reality, we have far better tools and information available than ever before. The missing link is interpretation, which can be filled in with a call to flight service. After dedicated study, pilots can also learn the nuances of weather science. Some pilots are natural weather nuts, with Intellicast.com locked in as their home page and The Weather Channel constantly playing on the family room TV. Even if you're not one of these amateur meteorologists, it pays to be a bit of a weather nerd.
Your goal is to mentally draw a three-dimensional picture of the weather from the data and know when that picture needs to be updated during the flight.
If you wish to avoid encountering IMC, you need to be aware of several key indicators in the information presented to you during a preflight weather briefing. The position of fronts and their movement give a rough idea of where and when lowering weather will occur. Specifically, look at the temperature/dew point spreads along your route. A close spread means that haze and fog are likely.
Fog can be tricky, as the visibility straight down through it tends to be far better than that along a diagonal. For example, you may easily make out the runway when overflying your destination airport. However, when you turn on final, the runway environment can disappear — just when you get low enough that you need to see the runway now.
Next, think of the terrain between the departure airport and the destination. If the area forecast describes an unstable air mass over the region and your route takes you over rising terrain, you can expect clouds to form in these areas before anywhere else. Rising terrain does not necessarily mean mountains: The difference in elevation between the Colorado-Kansas border and Denver (1,600 feet) is enough to form upslope clouds on the Colorado plains should the winds aloft be out of the east or southeast.
While you're looking critically at the data, try to determine which are from standalone automated systems (such as ASOS Level D) and those systems that are supplemented by a human weather observer (such as ASOS levels A, B, and C, or ATIS reports). These sites, along with the hours that the ASOS is augmented by weather observers, are listed in the airport/facility directory. Experienced weather observers say ASOS can issue unrepresentative reports when IFR and low-IFR conditions prevail, according to the Weather Strategies Safety Advisor published by the AOPA Air Safety Foundation.
On the flip side, ASOS stations give you an additional tool to use along the route. Periodically tune in nearby ASOS frequencies to stay up to date on local weather conditions. Be particularly alert for changes that take place ahead of or behind schedule when compared to the forecast. Low ceilings and visibilities that don't burn off by noon, as well as fronts that charge through before they were expected, signal that conditions could be more intense than originally thought. Landing or turning around before you get into the low stuff is a smart move in these instances, unless you can successfully file an IFR flight plan and complete the mission that way.
The human touch is as important in the air as it is in ground-based data. While the area forecast gives a big picture guesstimate of conditions along the route, your best info can come from other pilots. Solicit and provide pilot reports (pireps) whenever possible. And don't fall prey to superstitious thoughts that filing a pirep for a smooth ride and good vis will turn on the automatic bump machine.
As you gather information once the flight has launched, recognize that the go/no-go decision you initially made before takeoff becomes the continue question in flight. Making a no-go decision is typically easier than discontinuing a flight — especially as you get closer to your destination. So how do you know when the conditions are sinking to the point where you need to turn around?
One skill that eludes many pilots is judging distance in flight. If you need validation of this, recall the last time you heard someone call a two-mile final and subsequently waited for him or her to touch down five minutes later. Learning to judge in-flight visibility is just as tricky.
There are several ways to determine in-flight visibility, the handiest being landmarks such as towns or features a given distance away. Local pilots refer to a tower adjacent to Tri-County Airport near Erie, Colorado, as the "VFR stick" because it's about three miles from the field and nearly 1,000 feet tall. Section lines and highway markers are useful for gauging distance as well. Roads laid along section lines are one-half mile apart and can be found extensively from the Great Plains westward to the Rocky Mountains.
Speaking of the territory, also factor in what you're accustomed to — 10 miles' visibility out West makes you feel like the walls are closing in, but on the East Coast, it seems like ceiling and visibility unlimited (CAVU).
Go up with an instructor to practice in marginal or IFR conditions. Maneuvers should include basic attitude instrument flight, 180-degree turns, and situational awareness using terrain, navigation aids, and charts — including diversions to nearby airports.
An IFR flight plan
It seems obvious, but the best way to avoid continuing VFR into IMC is to operate on an instrument flight plan. Well, of course. But the reasons why run deeper than a simple change in the flight's definition.
Scheduled commercial operations in Alaska lean more heavily toward single-engine, single-pilot, VFR flights than do those in the lower 48 states. And commuter accidents in Alaska are also more likely to be classified in the VFR-into-IMC category than those in the rest of the country. Not only is there some performance pressure to continue flight into deteriorating conditions, but also, depending on the business, operators may be following air taxi regulations rather than the more stringent regulations for commuter airlines. One recommendation made by former NTSB Chairman James Hall to stem the tide of VFR-into-IMC accidents was to move these operations onto IFR flight plans whenever possible — though icing forces pilots to stay VFR for much of the year.
For a private pilot, the training required to get an instrument rating helps to alleviate the primary causes of accidents in IMC. You gain attitude instrument skills, navigation and diversion skills, and overall comfort flying in the weather. Even if you never plan to fly hard IFR, being able to file when the weather just might turn ugly lends a level of safety you wouldn't have on a VFR flight plan.
Instrument-rated pilots are lost in VFR-into-IMC accidents as well, because they don't file IFR when the conditions warrant, or they trust their attitude instrument skills to keep them not only upright but clear of terrain. One aspect of the problem lies in preparedness. Filing an IFR flight plan typically demands that the pilot at least look at the charts for the route in order to properly file and copy a clearance. Although it's possible to call for and receive a direct clearance, it happens infrequently enough that most pilots know better than to trust in getting the big D. In order to file legally, you need to be current as well, and that makes the operation another increment safer.
Perhaps the darkening shades of gray are best avoided by setting hard rules for ourselves. Get all the information available before your flight, and update that information often along the way. Acquire the ability to fly on instruments, and keep those skills sharp. File when it looks marginal, and don't be afraid to ask for a flight plan when the weather heads south in a way that wasn't forecast. And above all, don't underestimate the risks associated with flying into adverse weather (see "Wx Watch: The Rolling Go/No-Go," page 143).
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- Obtain weather from all available sources prior to the flight.
- Know the tools you can use to update weather information in flight: VFR flight following; flight watch or flight service; pilot reports; nearby AWOS, ASOS, or ATIS frequencies; and on-board weather radar or lightning detection equipment (with datalinked weather soon to come).
- Learn to interpret in-flight weather cues and deteriorating visibility.
- Acquire instrument skills in addition to those required for a private pilot certificate.
- File an IFR flight plan, and don't cancel IFR until a VFR landing is assured.
Common accident scenarios: VFR into IMC
- Departing VFR when the weather is below VFR minimums.
- Scud running along a well-known route.
- Improper judgment of deteriorating weather.
- Underestimating risks associated with flight into adverse conditions.
- Overconfidence in the pilot's ability to cope with adverse weather.
- Allowing social pressure from passengers to color decision making.
- Inadequate gathering of weather information prior to the flight.