Sight Unseen – Beating Bad Visibility on Base
By Robert M. Wright
Photo courtesy Karen Helfert
Two kinds of factors can create risk if a base leg is carelessly flown with a lack of situational awareness. These are environmental factors and aircraft design factors, and they can cause obstructions to vision on the part of departing aircraft. In teaching students it is generally recommended that the base leg be turned 45 degrees off the landing runway numbers at an altitude no lower than 300 feet below pattern altitude.
In general this allows for a sufficiently long final for the student, or low-time pilot, to stabilize the approach, and make the runway if the engine quits. These positioning and altitude limits usually allow the aircraft to be seen on the base leg by other aircraft, particularly those in the holding bay or at the hold short line.
A potentially serious problem can develop if the view of the base leg is obstructed or the base leg is flown very tight or too low, or a combination of both, all of which can be exacerbated by geographical factors. But since we’re all human and therefore creatures of habit, standard patterns are developed so we know where to expect other aircraft to be and govern ourselves accordingly.
We expect a base leg to be turned more or less at a certain position and flown at a certain altitude. That is where we look when we hear a radio call or are clearing the area at the hold short line. We need to be aware when we’re in a situation where we may not be able to see an aircraft on base. Likewise when flying, we need to pay attention to where we are on base and may not be seen by others. The following are several common situations:
Environmental Obstructions to Vision
Unobstructed views from a holding bay or hold short line may not exist. Trees grow and buildings get built. The pilot awaiting takeoff should be aware of the problem and exercise extra vigilance. The pilot flying needs to be aware of it as well and ensure that he avoids getting low so that the aircraft won’t be blocked from view by an obstruction.
Aircraft Design Obstruction to Vision
There you sit in the holding bay in a high-wing aircraft doing your run-up. Run-up completed, you move straight ahead to the hold short line lining up almost 90 degrees
to the line. You crane your neck to the right or left to see if anyone is on final, subconsciously noting (but not consciously appreciating) that the wing obstructs your view of the base leg. No one appears to be on final, so you take the runway and start your roll. Almost immediately you hear someone call final and shortly thereafter call a go-around in a disgusted tone.
The Tight Approach
Supporters of the tight approach argue that it’s more efficient, allowing more aircraft to land in a given amount of time, and puts the aircraft closer to the runway in the event of an engine out. However, too often the tight approach translates into a low base leg
preparatory turn to a short final which, when combined with environmental obstructions or aircraft design issues, creates a scenario where the aircraft on base can’t be seen until it’s on a short final.
At a minimum this causes a go-around. Worse, the landing pilot may try to “save” the situation with some risky low-altitude maneuvering (for example, S-turns) or will simply land behind the departing aircraft, trusting to luck that the departing aircraft will not have to abort. Worse still is the potential for the “straight down the runway” go-around where both aircraft are blind to the other’s position.
The latter is particularly dangerous where the departing aircraft is high powered or an LSA and is likely to climb rapidly in a short distance.
Minimizing the Risk
The risk can be minimized by the following practices:
- Departing aircraft should be aware of any obstructions to vision. Where obstructions exist, position the aircraft at an angle to the hold short line such that most of the base leg can be clearly seen. If necessary, make a 360 ground turn in the holding bay to clear the pattern.
- Landing aircraft should be aware of environmental vision obstructions and if possible fly the base leg at an altitude that keeps them visible. Avoid low base legs. Otherwise, make sure your radio calls keep departing aircraft properly advised.
- Aircraft on the base leg should take note of aircraft design vision obstructions such as a high-wing aircraft lined up 90 degrees to the hold short line. Low-wing aircraft, where the hold short area is on the downwind side of the runway, may also have obstructed vision if not properly aligned to the hold short line.
- If you’re flying a tight pattern, be particularly vigilant and always be ready for a go-around flown to the right of the runway – not over it – allowing you to maintain visual contact with the departing aircraft.
- If you’re taking off and hear a go-around called, don’t climb rapidly. Control the angle until you’re sure the other aircraft is clear.
- Fly defensively. Always assume the other aircraft will do the wrong thing.
Robert M. Wright is a CFI at Chesapeake Sport Pilot, located at Bay Bridge Airport, Stevensville, Maryland. This article was originally published by Mentor, the magazine of the National Association of Flight Instructors.