Masters Theses

Date of Award

8-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Aviation Systems

Major Professor

William D. Lewis

Abstract

This thesis examines the feasibility of using steep Global Positioning System (GPS) approaches in Instrument Meteorological Conditions (IMC) for the military. The experiments were conducted in the UH-60A/L Flight Simulator at Fort Hood, Texas, with a crew of two pilots. The experiment investigated GPS instrument approach tasks with evaluation subtasks of: (1) a level flight conversion to approach airspeed configuration and glide slope intercept, (2) glide slope and localizer tracking, and (3) completion of the landing following breakout. Qualitative and quantitative data was collected on aircraft performance and handling qualities. Handling Quality Rating (HQR) were assigned to approach task and written comments on flight control inputs were collected.

The glide slope angles were varied, starting shallow and ending with a steep approach configuration. The glide slope angles were 10, 9, 8, 7, and 6 degrees. Each pilot flew each approach at various airspeeds, 120, 100, 90, 80, and 70 knots. Once the aircraft broke through the 100-feet Above Ground Level (AGL) weather ceiling, the pilots had to maneuver the aircraft to safely land the aircraft at the designated location in the marshalling area. The objective was to bring the aircraft to a 10-feet hover over the designated GPS landing point safely.

The results demonstrate the ability of the aircraft to safely fly GPS approaches into IMC conditions. The optimum approach combination was 7-degree glide slope at 70 knots. The worst configuration for all the approaches was ID-degree glide slope at 120 knots. Any approach above 10 degrees at 120 knots to 100 knots will result in major deficiencies with control being lost during some portion of the required operation during breakout. An approach below 7 degrees glide slope angle does not provide safe aircraft clearance for obstacles. Evaluations revealed serious problems with pilot's loss of intended landing spot from the cockpit obstructing Field Of View (FOV) during aircraft deceleration for approaches above 8-degree glide slope and above 90 knots.

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