by Harold Green
Virtually every student pilot has asked, “Why do I have to learn ground reference maneuvers?” The other day, while staring out the window as my student attempted to turn a lopsided ellipse into a circle with a properly located center, I had an opportunity to consider how extensively ground reference maneuvers affect our flying. The answer is “quite a lot.”
First of all, on a general basis, all flying is a ground reference maneuver. After all, we don’t go from one place in the sky to another. Flight always begins and ends on the ground; frequently at two different places on the ground. Hopefully where, and approximately when, we intended to arrive. In order to do this it is necessary to be able to correct the flight path to track the course even in windy conditions. While this is obvious, we often don’t think of it as a ground reference maneuver, but it is, whether we are flying VFR or IFR. Remember rectangular patterns?
When it is time to land, hopefully where, and kind of close to when we intended, it is again required to contend with ground reference maneuvers and wind correction. The goal is to put the airplane on the runway at a pre-determined point. That means awareness of our position on the ground and our path over it. The wind makes it necessary to adjust the ground path to land where we want. If there is a headwind on the base leg, our turn to final must be adjusted to arrive at the planned touchdown point. Generally, this means delaying the turn onto final more than if there was no crosswind. If there is a tailwind on base, it is necessary to turn on to final earlier than if there isn’t a tailwind, so as to avoid overshooting the final path.
Failure to do this, coupled with failure to recognize the need to go around, can result in a very tight turn close to the ground. If this happens and the pilot kicks in inappropriate rudder, the result can be a spin or snap roll without room to recover that close to the ground. Several people are killed this way every year.
Remember S-Turns? Therefore, when given a choice of landing direction, as with a 90-degree crosswind, it would be wise to select the path, which offers a headwind on base leg.
Then comes the need to descend on final. Again, the issue here is groundspeed. Proper procedure calls for holding a specific airspeed on final to avoid the possibility of stalling while enhancing pilot judgment. (A stall is NOT a ground reference maneuver.) Now since there is most likely a headwind component, groundspeed is slowed by the amount of headwind. This means that the stronger the headwind, the longer it takes to get to the runway. Since descent rate is a function of airspeed, the longer it takes, the more altitude that will be lost before the runway is reached.
Like a VFR landing, an ILS approach is another ground reference maneuver. Of course we set up an approach speed and then attempt to keep that elusive horizontal needle in the center of the dial. The issue here is that the glide slope defines a slope relative to the ground. Unlike a VFR landing, both the beginning and end of the glide slope are specified. Therefore, performance is based on feet per mile, not feet per minute.
A quick look at the descent table on the back cover of the government approach plates shows some interesting statistics. For example, a 3.00-degree glide slope requires a descent gradient of 318 feet per minute (fpm). At 90 knots, this requires a descent rate of 478 fpm to remain on the glide slope. Now factor in a 15-knot headwind and a groundspeed of 75 knots, the descent rate must be only 398 fpm. If there is a tailwind, the rate becomes 557 fpm. (This could happen when the only approach with low enough minimums is an ILS from which a circle to land is planned.) It is wise to remember that this table can also be used to determine the rate of ascent required to meet the obstacle clearance requirements stated under obstacle departure procedures. Thus, if the departure procedure calls for maintaining a climb gradient of 475 feet per nautical mile and your groundspeed is increased by a tailwind, then the rate of climb must also increase.
For example, if the climb speed is 90 knots and a 15-knot tailwind is encountered while climbing, the rate of climb must go from 715 to 835 fpm. Depending on density altitude, aircraft weight and aircraft basic performance, this could present a challenge.
Holding patterns are also ground reference maneuvers. If the pattern is GPS based, then it is obvious since GPS holds are mileage defined. Holds which require a specific time on the inbound leg are also ground reference maneuvers since they require a specific path along a radial or bearing. Furthermore, the time on the outbound path must be adjusted to produce a specified time on the inbound leg — usually one minute. The track of the pattern varies with the direction and extent of the crosswind encountered. This is emphasized by the fact that turns when in IMC (Instrument Meteorological Conditions) are standard rate regardless of wind direction or velocity. Thus, unlike our turns around a point, the rate of turn does not change to compensate for the wind.
When turning away from the wind, the radius of the turn increases, and when turning into the wind, the radius decreases, resulting in a lopsided racetrack pattern.
As an example, using a calculation provided by CSGNetwork with an airspeed of 90 knots, and assuming the wind is a direct 20-knot crosswind, the radius of turn varies from 3389 to 5064 feet. Note: This is an approximation only because it does not take into account that the crosswind direction varies as the aircraft turns. However, as a first approximation, it will serve to illustrate the point. Because of this variation in radius, the rule of thumb for wind correction is that “Outbound wind correction should be approximately three times the inbound correction.” This is a good starting point. This does illustrate what happens when wind compensation is not employed as it is in those infamous turns around a point or S-turns across a road.
The conclusion of all this is that ground reference maneuvers are fundamental to most aspects of flying. Those pilots who have developed a good understanding of the whys and wherefores of ground reference maneuvers seem to have an enhanced spatial awareness, and a better understanding of the operations discussed herein. They understand landing pattern operations and wind compensation, whether they are operating in a non-towered or towered environment.
Today’s curriculum for private pilots has reduced ground reference maneuvers compared to earlier times. The S-turns, turns around a point and rectangular patterns are a good start, but for example, pylon eights are no longer required. That is not necessarily bad, but I do believe that some element of training has been lost.
Back in pre-historic days, we had to do pylon eights around points and across roads. Even lazy eights with the need to see the nose at maximum pitch at 45 degrees and the nose coming level at the 90-degree point, were informative, if not frustrating. These were good exercises and I still teach some of them to students who need a new challenge to maintain motivation. There is also a reason that the commercial ticket contains more advanced ground reference maneuvers, such as turns on a point and pylon eights. Perhaps it would be advantageous to include some ground reference maneuvers in a biennial fight review (BFR). Occasionally one finds a student who enjoys such maneuvers.
EDITOR’S NOTE: Harold Green is an Instrument and Multi-Engine Flight Instructor (CFII, MEII) at Morey Airplane Company in Middleton, Wisconsin (C29). A flight instructor since 1976, Green was named “Flight Instructor of the Year” by the Federal Aviation Administration in 2011, and is a recipient of the “Wright Brothers Master Pilot Award.” Questions, comments and suggestions for future topics are welcomed via email at harlgren@aol.com, or by telephone at 608-836-1711 (www.MoreyAirport.com).
