Don't risk it
Adhere to your own safety margins
All things in aviation share one common ingredient with everything else: safety in the form of planned margins. The airplane itself has a 1.5 safety factor over and above the G-load where things start bending. We flight plan so we have a minimum of 45 minutes of fuel in reserve. Instrument approaches have published minimums. Most of us know margins are a good thing. Unfortunately, a few of us ignore margins altogether, while others either don’t understand what constitutes a viable margin in all situations or abuse the concept and overdo it.
Put your mind to it. First, there is the basic concept of the margin and then there is the practical application of that concept.
The basic idea is the need to protect ourselves in case things don’t go as planned. And this applies to all regimes of flight in all situations in all airplanes. One of the classic indications someone doesn't really understand the concept of margins is when he says something such as, “I think I can make it”—and we’ve all heard ourselves say that or something similar. The clouds look a little lighter over there, so we push on. We’re convinced the tank holds a couple gallons more than the gauge shows, so we push on. The airplane is known for its gentle stall characteristics, so what’s the harm of approaching a few mph slower than we’ve gone before?
The next time you hear yourself say you “think” you can make it, say this to yourself: OK, so what’s the downside if this doesn’t work out? What if I’m wrong and can’t make it. Then what?
You know you’re cutting your fuel a little close but you “think” you can make it. Now, do the alternative: What happens if it turns out you really don’t have enough fuel? If you’re even a tablespoon of fuel short of enough to make it, you crash. The consequences of something not working out are always bad. Nothing good ever comes from running out of fuel, stalling short of the runway, or pushing into rapidly decreasing visibility.
Now that we’ve established that our mindset should always be to build in a safety margin “just in case,” what is the definition of enough margin and is there such a thing as building in too much margin? The answers are neither clear nor universal to all situations.
Is there such a thing as too high? Let’s take altitude on a cross-country as an example of setting margins. Is there such a thing as too low? Of course there is, but how do you define it? A number of factors affect the answer. For one thing, if your propulsion unit decides to stop propelling, you are better off at 1,000 feet than 500 feet (not to mention unseen towers and such). As far as that goes, if you ever do lose an engine, you’ll wish you were at 10,000 feet agl.
When it comes to picking a cross-country altitude, sometimes the topography forces some decisions on you. We don’t want to just barely sneak over a mountain range. We just don’t know what kind of wind conditions we’re going to encounter on either side. So, we build in a wide altitude margin. We also cross at “glide down altitude,” the altitude at which we can lose an engine and still have enough altitude to glide down to relatively safer terrain while looking for a landing spot. Incidentally, some of the decisions are regional in nature: You obviously don’t worry about glide-down-altitude in Nebraska as much as you do in Colorado or Utah.
VFR in questionable weather needs bigger margins. How much margin do we build in when weather is a factor? The short answer is “plenty” because we never know exactly what we’re dealing with or what is just a few miles ahead. If we’re VFR under the clouds and they start closing in, we are essentially flying blind. This is when margins attached to personal operating limitations should be cast in concrete and brought into play.
Yes, the federal aviation regulations lay out visibility minimums, but that’s just what they are—minimums—and we don’t want to work at minimum margins. Besides, not many of us can accurately guess what is a mile or three miles. Plus, visibility/ceiling minimums are almost all lower than it’s wise to be out blundering around in—especially if you’re new to flying. When it comes to ceilings and visibility, give yourself a wider safety margin, because there’s always a big chance that ceilings and visibility will deteriorate.
Incidentally, it would be interesting to see statistics about “flight into known IMC conditions” before and after GPS was introduced. It could be argued in those kinds of marginal conditions a pilot without GPS, who was trying to navigate either by pure pilotage or VOR (which disappears at lower altitudes), would do a 180-degree turn out of weather faster than a person with GPS. When you don’t know exactly where you are, you’re more likely to turn back to a known position. With GPS, you know where you are and you have the Nearest Airport button. If the airport appears behind you, great, because two things happen at the same time: a 180-degree turn and a known heading toward an airport that is likely to have better conditions. If the airport appears somewhere ahead, it dangles a carrot in front of you. No matter how close it is, if conditions have been getting worse, it’s a gamble to push toward that airport. We don’t know what lies ahead but we do know what’s behind us. It’s a tough decision to make and it is very much dependent on the situation at that exact moment.
The key lies in how tightly we’re going to hold ourselves to keeping the margins we’ve set: When we see a margin disappearing, we aren’t going to let get-there-itis talk us into violating the personal rules we’ve set. We do a 180.
Similar margins should exist when flying VFR on top. We tell ourselves the destination should be far better than necessary; if it decides to go downhill, it has a long way to go before it’s closed in. There isn't a more sickening feeling than being on top without an instrument rating and having the radio tell you that your destination just went IFR. Basically, be a weather chicken and set your personal margin limits so high that you’ll never get caught under or over weather.
And then there is airspeed on approach. Flying final at a higher airspeed than recommended in the pilot’s operating handbook is not safer. Yes, if you’re carrying a little extra to cover half of a significant gust spread, then you’re doing the right thing. But, if POH-speed-plus-10-knots is your usual modus operandi, you’re taking safety out of the landing equation. Oh, sure, if you’re fast on approach, you’re not going to stall, but you’re also not going to put the airplane on a given spot on the runway because of the speed-induced float. In fact, you have no idea where it’s going to land. It’ll come down when it feels like it. Coming over the threshold fast could be considered annoying, if not dangerous, for a number of reasons:
- It takes away your ability to land the airplane accurately.
- Getting it to slow down enough to land without ballooning is difficult.
- If we lose patience and put it on prematurely, it’ll likely be nosewheel first—and we’ll have a lot more energy to ablate than we need or want.
- The wind has that much more time to mess with you.
Three or four knots fast isn’t the end of the world, but anything approaching 10 knots will just give you heartburn. The practical test standards (PTS) say that it’s FAA-acceptable to be 10 knots fast and five knots slow, but neither should be considered OK. If you think being five knots slow is OK, then you’ll soon think seven knots is OK. Then eight. You’ll lose both the incentive and the skill to control speed and there’s the possibility that at some point you’ll be working in a dangerous area as your judgment and skills deteriorate.
Same thing with being fast: If you are in the habit of zooming over the threshold, the day will come when it’s critical that you land shorter than usual and you’ll find that you can’t do it. Extra speed works very much against you in those situations.
There’s no such thing as too much fuel. The 45-minute-reserve concept is a good one, but it’s critical that on each trip we ask ourselves a simple question: Is 45 minutes actually enough? Geographic region and weather conditions affect the answer.
In the eastern half of the country—especially near the coast, where you can spit in any direction and hit an airport of some kind—45 minutes lets us cover a lot of escape routes. At the same time, in the East, a pilot is more likely to be trying to outfly questionable weather as visibility comes down. So, is 45 minutes enough? Maybe each leg should be shortened enough to make that an hour reserve.
In the western half of the country, airports can be spread out so far that 45 minutes might not even get you to another airport. Plus, aircraft based in the West seem to come equipped with at least a 20-knot headwind at altitude, so they are almost never able to go as far on a tank of avgas as they hope they will. This is when an hour reserve is almost mandatory, depending on the specific trip. Also, in the West, thunderstorms are more likely to pop up, forcing big detours. When turning off course on a detour, peace of mind is looking down and seeing that a lot of fuel is left.
Every pilot approaches his flying with a built-in way of thinking that is unique to him. But at no point should we forget how hostile the environment in which we’re operating can be. Margins keep us safe.
Weather: Not tonight, dear
Is anything dumber than scud-running? Well, maybe one thing: Doing it in the dark.
We don’t know why the pilot of a Piper Comanche felt he had to get home to Omaha from Chamberlain, South Carolina, that Sunday night in November—or, for that matter, why he didn’t decide to leave earlier. We do know that he took off just before sunset on a 210-nm trip even though it was only marginal visual meteorological conditions at both his departure point and his destination—and instrument meteorological conditions at
several stations in between, where ceilings had remained below 900 feet all day and the temperature was within two degrees of the dew point. Of course, it’s possible he didn’t know; he didn’t file a flight plan, and there’s no record that he ever got a weather briefing.
The terrain in eastern Nebraska is gently rolling, not flat. Shallow declines separate low hills topped by radio towers, wind turbines, and trees. In the end it was a tree that got the Comanche, shearing the right wing from the fuselage and scattering airplane parts and personal effects for 800 feet until the final impact snapped the cabin back to the tail. The pilot and his passenger died on the spot.
If he really did have to get home that night, the crucial failure of his flight planning took place long before he launched into the setting sun under a 1,700-foot overcast. Passing up earlier opportunities to get home in better weather left him depending on luck, not foresight—never a reliable flight plan.
Fuel: Don’t make me pull over
Running out of gas is a nuisance any time, but at least in a car you can pull off the side of the road. In an airplane, it’s almost never that convenient—even when you have the advantage of being able to put it into a farm field rather than a forest.
After a total loss of engine power, a Piper Cherokee 180 made a forced landing in an Iowa cornfield on September 23, 2009. The airplane touched down under control, and its landing gear cut tracks through the corn for about 100 feet before the nosegear dropped into a ditch, flipping the airplane onto its back. Blunt force trauma killed all three men on board. They’d left Fort Atkinson, Wisconsin, about three hours earlier on the first leg of a hunting trip to Winner, South Dakota.
Investigators found one cup of fuel in the left tank, two and a half cups in the right, and none in the carburetor. They also established that the pilot and his friends knew they’d need to stop for fuel; back at Fort Atkinson, a witness had heard them agree that “filling the tanks to the tabs” wouldn’t give them enough fuel to make it all the way to Winner, and a relative recalled hearing that they’d planned to leave with partial fuel in to improve takeoff performance in warm weather with a high density altitude.
In the last half hour of the flight, they passed up at least five airports where fuel was available. The crash site was just three nautical miles from a sixth, the field at Sheldon, Iowa. Sheldon’s page from the Airport/Facilities Directory was clipped to a kneeboard found in the wreckage. Just a little more margin for error would have been enough to avert this tragedy.
David Jack Kenny is manager of aviation safety analysis for the AOPA Air Safety Institute.
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