Five critical things to understand
There are two kinds of losses of aircraft control: low speed and high speed. The low speed version has been the hottest button of late with almost massive attention from the government and the associations. The NTSB has even made the prevention of loss of control in general aviation one of the most wanted transportation safety improvements for 2015.
There is nothing new about this. Loss of control has been the number one cause of fatal private aviation accidents since the beginning of flying time. The phenomenon is actually one of the things that prompted my father to start Air Facts in 1938 and we have been talking about it here since that beginning.
Rather than rehash all the information that has been cranked out by the government and the associations, let’s just have a discussion of the problem and how to avoid it. It is really pretty simple. A low speed loss of control comes when a pilot doesn’t allow the airplane to fly. Whether the accident is characterized as a stall/spin or simple loss of control usually depends on the altitude of the airplane when it departed from controlled flight. Most often, it happens at an altitude too low for a spin to develop before the ground intervenes.
Know the Booby Traps
Low speed accidents usually happen when the airplane is being maneuvered close to the ground. There is no way to take off and land without doing just that so it is obvious these are areas of higher risk. Maneuvering at low altitude for other purposes is best left to those doing special-purpose flying like crop dusting, patrol, and air show flying.
The risk in low altitude flying is lowest on calm, clear days when the airplane is being operated from an airport that is of more than adequate size for the available performance.
The risk is highest when the available performance is marginal and weather is a factor. Weather in this context is mainly gusty surface winds, related wind shear, and high density altitude.
I am going to put wind first because I think it has not gotten enough attention in the current discussion.
A gusty wind makes the airspeed vary, sometimes wildly and quickly. In low altitude operations at what seem like proper attitudes and power settings the airspeed excursions and turbulence can sometimes make the stall warning squawk. The stall warning systems simply tell when the airplane is approaching the critical, stalling, angle of attack so that momentary squawk is a plain message about a trespass into a risky area.
The holy number on approach airspeed is 1.3 Vso (some airplanes show 1.2 for short field approaches but that is questionable). For the purpose of illustration, let’s say the airplane stalls at 60 knots so that would make Vref 78.
Gusty wind is wind shear in its purest form as the wind is changing in direction and velocity with time and is doing so rapidly. If you are flying final at 78 and the wind is 20 with gusts to 35, that 15 knot variation could set you up for a 15 knot variation in airspeed that could put you close to a stall. In light airplanes, that is usually momentary, thus the short squawk from the stall warning, but it can cause a substantial sinking spell.
There are a lot ways to deal with gusty wind. Some add the value of the gust to Vref, some add half the value. I always liked to add enough so as the airspeed is gyrating wildly the lowest excursion would be close to Vref. If there is a sinking spell, the way to deal with that is by adding power. If there is no power the best thing is to reduce the angle of attack if necessary to keep the airspeed on a safe value.
Angle of Attack Instrumentation
I mentioned angle of attack a moment ago and angle of attack (AOA) instrumentation for light airplanes is at the forefront of much of the current discussion. Many in government and at the associations are starting to sound like commissioned salesmen of the devices.
Understanding angle of attack is of vital importance but I think the instrumentation is of less importance in light airplanes. It might be nice to have and certainly every pilot who has to have the latest gadgets will buy it but all can fly quite safely without it.
I just mentioned the airspeed jumping about wildly on a gusty day. Guess what. The AOA indication will too. I think it would create a headache to think all the way through the question of the relationship between indicated airspeed and angle of attack in gusty conditions and the conclusion might just be that they both move about a lot.
There are not many loss of control accidents that begin with the airplane on a wings-level final approach. There are a lot more when the airplane is being maneuvered to that final approach or when everything is wrong and a go-around is required.
In most accidents the event begins when a pilot flies past a point in a flight where the risk skyrockets. Salvation is in blowing the whistle before passing that bad spot and regrouping. In other words, don’t fly into a situation where the likelihood of a low speed loss of control increases.
One critical scenario comes on a windy day with a downwind condition on base leg and a crosswind on the runway. The danger spikes when the downwind on base causes an overshoot of the final approach course. The natural reaction is to steepen the bank to hurry the turn. If the bank is in excess of 30-degrees, the stalling speed increase is rather dramatic. Also, the visuals are not good because at least at the start of the turn the speed over the ground appears fast, which might create the illusion of higher than actual airspeed.
There are ways to handle this. First and foremost is to abandon any approach that can’t be flown while limiting the bank angle to 30-degrees. Once that is done, another pattern can be flown with downwind substantially farther from the runway or the pattern can be reversed to allow for a headwind instead of a tailwind on base leg. I know, non-standard patterns are a no-no but they beat risking a low speed loss of control.
I mentioned pilots’ not allowing the airplane to fly. We have all heard references to natural pilots and talk of those who really have a feel for the airplane. There is no precise definition but I think that describes a pilot who is always aware of how his control inputs are relating to the available margins and how the airplane is reacting to those control inputs. An airplane flies within a defined envelope and the margins are simply how far you are staying away from the edges of that envelope.
An airplane always flies at a trim speed for its current situation. To go slower than the trim speed the pilot has to use back pressure on the elevator control. Having the feel of an airplane means knowing how much and how rapidly the airplane is being moved toward the stalling angle of attack.
A hackneyed old saying about the elevator is illustrative of this: “Pull back a little to make the houses smaller, pull back more to make them rotate and become quickly bigger.” Knowing when to quit adding back pressure, or when to relax it, is the key.
The elevators are most often considered when control feel is discussed but the ailerons are important because they too will communicate with you during low altitude maneuvering flight. Airplanes have an over-banking tendency and if a lot of opposite aileron has to be held against a bank that wants to steepen, the airplane had been flown into a bad place. It’s time to reduce the angle of attack and level the wings.
Aileron deflection can cause an airplane to yaw and that is one of the requirements for an airplane to spin if stalled. Many airplanes can actually be spun using aileron alone. The spin will be in the opposite direction with, for example, full right aileron at the stall leading to a left spin. I once mentioned this to a manufacturer’s test pilot and he said no way. I took him for an airplane ride and spun his little darlin’ with my feet flat on the floor.
Go back to that steep turn to try to line up on final, throw in a good level of turbulence and a pilot who tends to fight turbulence with equally abrupt control movements, and the stage is set. In that scenario the pilot has no way of knowing how the rapid control movements are related to the developing situation. A pilot who uses the controls gently but positively has a better chance of developing that old feel for the airplane.
The main thing to remember about the rudder is to never use it to make a banked airplane turn more rapidly. Rudder is best used to keep the airplane in coordinated flight, or, to keep the ball in the center. If a lot of aileron is being held against a turn, the ball won’t be in the center. It’ll be away from the turn to show that the airplane is skidding. If you use rudder pressure in the direction of ball deflection, or, step on the ball, that will move the airplane toward coordinated flight and the wings will also move back toward level, or, away from trouble.
Rock & a Hard Place
Pitch and power go together, Pitch up and add power to climb, for example. When power is removed from the picture the plot thickens and can do so rapidly. This is what happens in an airplane when the power fails. When the energy being used to propel the airplane goes away then the only energy available is altitude and airspeed. There are a lot of low speed losses of control as airplanes are maneuvered for the forced landing that follows a power failure. Make no mistake, engines do fail and unfortunately the incidence of this happening appears to be on an upswing.
Before going into the forced landing, I will digress for a moment.
That’s what paratroopers used to shout when they hit the silk. It was to show they were not afraid. I wonder if a Cirrus pilot has ever shouted Geronimo when deploying the airframe parachute.
There were a couple of notable Cirrus chute uses recently. In both cases, the engine failed and in both cases the pilot apparently decided to use the chute instead of fly to a conventional forced landing.
Is that a manly action? Absolutely. If a pilot has any doubt about a situation and has a chute available, it should be used. The insurance folks would probably not like this because the average hull loss on an average forced landing is likely lower than after a chute arrival but that’s tough. The pilot’s job is to minimize risk. I have nothing but admiration for the chute-poppers and feel that what they did was get their money’s worth out of the device. If, after that, they want to buy another Cirrus and fly on, fine. If they decide that piloting wasn’t really that enjoyable, fine too.
The Real Thing
Because few pilots make power-off approaches, a forced landing involves a type flying that is not done often. The days of practicing power-off spot landings are pretty much gone and that is precisely what a forced landing is.
I mentioned that a stall involves a pilot not letting the airplane fly. It can also involve the pilot asking the airplane to do something that it is unable to do.
There is no such thing as stretching a glide. It just doesn’t work. If a forced landing is set up and then goes bad, the survival mode has to become maintaining a normal glide speed with the wings level except for minor adjustments. The conclusion starts when the airplane contacts whatever is coming along and begins the process of stopping. The stop doesn’t have to be spread over many feet to be survivable but it does take a little distance so brick walls are not good.
The simple fact is that crashing under control is many times more survivable than crashing out of control.
While maneuvering for a forced landing the 30-degree bank maximum from traffic pattern should be observed.
A go-around is a critical maneuver and is the starting point of many loss of control accidents. John Zimmerman’s recent post on this subject elicited some good comments.
One person mentioned trim in a comment. The two schools of thought on trim are that the airplane should always be kept in trim, that is, no elevator pressure required. The other school is that in many situations the airplane is best flown out of trim.
On an approach with the trim speed a bit higher than the approach speed, you are using a little back pressure to maintain the desired airspeed. I personally think that this is good because the airplane is telling you what you are doing and it would intensify the message about being slow if back pressure were added that would move the airspeed below Vref.
A lot of loss of control accidents start happening soon after takeoff. The classic one comes after an engine failure during initial climb followed by a dramatic attempt to turn around and return to the runway. That is about the most dangerous low altitude maneuver of all.
Conventional wisdom has always held that if the power fails on initial climb, the best thing to do is establish a normal wings-level glide, survey the area ahead for the friendliest parking spot that won’t require much maneuvering, and then make the most of the rest of your day.
On departures with no mechanical problems but with marginal performance given the runway length and obstacles, the best you can do is fly at the best angle-of-climb airspeed and hope that the available performance will be enough. If not, controlled flight into whatever is there offers the best chance of survival.
In the title I mentioned five critical things to understand on this subject. I haven’t been specific on this so, in closing, I’ll give you a list.
- Always question whether or not you are developing a feel for flying. Are control pressures and positions communicating with you? If not, make that acquaintance.
- Avoiding trouble means anticipating when the airplane is moving into an area of higher risk and taking the necessary steps to counteract that risk. That might be thought of as an aeronautical version of getting the hell out of Dodge.
- Good planning can go a long way toward eliminating risk. That would mean having a plan for every eventuality and following that plan. Then if there is a downwind on base leg or the power fails on initial climb, the first thought will not be, “What do I do now?”
- Practice the tough stuff. If you haven’t flown a go-around in a while, go out and do a couple. Get used to all the trim changes and aircraft reactions while going from the approach to the climb configuration. Study your use of trim to make certain it doesn’t put you at a disadvantage. One other thing on going around: There is a long history of fatal accidents when a go-around is attempted after an initial touchdown. That suggests that if the wheels contact the runway, the best deal is to try to stop as gracefully as possible.
- Respect the performance limitations of the airplane. The required distances to take off and land in the POH are for a test pilot flying a new airplane in ideal conditions. Add at least 60-percent to those numbers.
In closing, a wish: May you never run out of airspeed, altitude and ideas at the same time.