Undershoot Control

This lesson shows how to recognise and manage a developing undershoot.

Looks like an undershoot from here with the airbrakes open two-thirds

Learning Points

An undershoot will leave you short of the intended landing area. It can be recognised by seeing the Reference Point (RP) too high, or moving up, in the canopy. The top picture shows the RP well up in the canopy compared to where we want it – we established in the previous lesson that in these circumstances we should hold the RP just below the string in our view.

If the undershoot area is unlandable, or you want to land in the chosen area, you must respond and correct it.

When you recognise an undershoot developing, close the airbrakes. Settle the glider at the intended approach speed, and fly forwards to intersect the two thirds airbrake descent path which will be in front of and above you. When the picture looks correct, open the airbrakes to two thirds, settle again at the approach speed and assess the situation. Adjust if necessary. The second picture shows that we have intersected the two thirds airbrake descent path, and have the RP held in the right place in the canopy.

Now on the correct approach path with two thirds airbrakes

Scenario and Demonstration

The demonstration is one of a set on Approach Control. They all start a long way out to exaggerate the points being shown. The intended landing area is the bright green grass, and you are landing into a 10kt headwind. The RP is the nearest edge of landing area.

This demonstration shows the early approach with no airbrake as we are a long way out. We open two thirds airbrake when it is obvious we are going to overshoot the airfield. As the approach continues we can see the RP moving up the canopy. Attitude must be held constant to make this apparent. We have opened the airbrakes too soon, so we close them. We fly forward, waiting to intersect where we now judge the two thirds airbrake descent path to be. When we reopen the airbrakes and resettle, the RP remains constant in the canopy so we know we are on the desired path. Continuing as we are, we round out just above the RP and land where we planned.

Recognising and controlling a developing undershoot

The video is best viewed in YouTube in Full Screen mode, to easily see the on-screen messages during the demonstration. Use view, pause and rewind as needed to grasp the content and timing of the messages displayed, then focus on the action.

Performing the Exercise

Line up with the airfield, trimmed for approach. Open the airbrakes a bit too soon and watch as the undershoot develops. Note how the RP moves up the canopy as you descend too soon. Close the airbrakes and fly forward. Reopen them when you judge you’re on the correct descent path to round out at the first cross track.

Further Reading and References

Gliding From Passenger to Pilot, 2nd Edition: Page 108-111

BGA Instructors’ Manual, 4th Edition: Section 2, Chapter 12

BGA Instructors’ Reference Cards: Ex 12c

BGA Gliding Basics – Approach and Landing