AOPA Pilot Magazine - February 2018 - 89

An attractive alternative to the traditional
rectangular pattern is to replace the squared
base leg with a constant, gentle turn from the
end of downwind onto final.
from the standard prescribed in UND's
procedures manual. The spacing between
the downwind leg and the runway, and
the point at which the turn from downwind began, were the same as used in the
rectangular pattern. Target power settings
and airspeeds also were essentially identical. While the rectangular track calls for
10 degrees of flaps at the abeam point and
20 degrees once established on base, the
rounded-base turn method calls for extending the flaps to 10 degrees early in the
downwind, then to 20 degrees just before
the turn. A final configuration change to full
flaps was permitted once the turn was complete and the aircraft was established wings
level on final. The primary difference was
the lack of a wings-level rollout between
leaving the downwind and entering final.
One of the lesser-known features of the
G1000 is its flight data recording capability,
which allows almost every measurable aspect
of the flight to be recorded approximately
once per second. This study focused on airspeed, bank angle, pitch attitude, and vertical
speed. An additional variable, which required
some deeper analysis, was the alignment of
the aircraft with the runway upon completion of the turn to final. This was determined
based on the frequency and intensity of
changes to bank angle that occurred after the
aircraft rolled wings level on final.
This project was considered a pilot
study, a potentially confusing term in the
field of aviation research. It means that the
study was primarily intended to serve as
proof of concept for a future full-scale version. The results clearly demonstrated the
feasibility of using onboard data logging to
measure the stability of an approach path
and detect misalignment with the runway
on final. Analysis of 16 rounded-base turn
patterns flown by UND instructors showed
impressive consistency of airspeed, pitch,
bank angle, and descent rate, while data
from pattern work on 16 randomly selected
training flights were more variable.

Although the presumed differences in skill
between students and instructors make a
direct comparison uninformative, prospects of obtaining conclusive results from
a properly randomized comparison using
this methodology are strong.
Reactions to the idea of the roundedbase pattern within the community have
been varied. One common criticism is the
assumed degradation of safety caused by
a supposed inability to check for traffic
on final while banked during the downwind-to-final turn. A further concern is the
wisdom of making configuration changes
while the aircraft banks. The visibility of
traffic on final will need to be investigated
in a full-scale research project, but instructor comment from the UND study suggests
that the shallow bank angle used in the
turn combined with the practice of checking for traffic before beginning the turn
largely avoids this problem. Unease regarding configuration changes while banked is
easily dismissed, as the procedure tested in
this study restricts configuration changes
to before and after the turn, with none
made while banking. Additional aspects
of the rounded-base pattern that merit
investigation include integration into
tower-controlled airspace, evaluation of
the procedure using a variety of aircraft,
and analysis of a constant upwind-todownwind turn.
The evidence is not yet sufficient to
establish the rounded-base pattern as
preferable to the traditional rectangular
pattern. It is safe to say, however, that it
deserves additional investigation in a study
large and robust enough to reach definitive
conclusions.
AOPA
LEWIS ARCHER is a professor at the Uni-

versity of North Dakota and was the lead
researcher on the rounded base-to-final
research. DAVID JACK KENNY is a freelance
aviation writer and former statistician for
the AOPA Air Safety Institute.

www.aopa.org/pilot AOPA PILOT | 89

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AOPA Pilot Magazine - February 2018

Table of Contents for the Digital Edition of AOPA Pilot Magazine - February 2018
