Assessment of the AH-64D Longbow Apache's qualities for instrument meteorological conditions/instrument flight rules flight

by Meely, Michael Jesse.

An assessment of the handling of the AH-64D for flight in IMC and under IFR was conducted. Testing was performed in the configurations listed in table 1 and under the conditions presented in tables 3 and 4. All test objectives were met. IMC mission maneuvers with all systems working resulted in satisfactory handling qualities with no excessive compensation required from the pilot (altitude and attitude holds ON). However, as the aircraft systems were progressively degraded the workload for the evaluating pilot increased significantly. The high workload coupled with the absence of a vertical speed indicator (VSI) and torque indication during an AC failure and the observed errors in the standby altimeter and airspeed indicators would most likely prevent flying a successful unusual attitude recovery, an airport surveillance radar (ASR) approach, or a precision approach radar (PAR) approach. The inadequacy of the standby instruments is a deficiency. The aircraft’s longitudinal gust response with FMC OFF required extensive pilot compensation to maintain altitude and airspeed within adequate parameters, further increasing the overall pilot workload, and is a deficiency. Additionally, the aircraft’s battery life does not meet the 30min requirement for IMC/IFR flight that would be required in the unlikely event of an aircraft AC power failure and results in a deficiency. Engineering maneuvers conducted to quantify the handling qualities of the AH-64D with FMC OFF confirmed the high pilot workload and extensive compensation required. These maneuvers revealed an oscillatory divergent long-term mode, an oscillatory divergent lateral-directional oscillation (LDO), negative spiral stability when banked to the right, and significant coupling between pitch and roll. While conducting these maneuvers, excessive instrumentation lag was observed in the standby altimeter during climbs and descents. This resulted in errors of up to 300 ft between boom data and the standby altimeter. The excessive observed instrument lag and inaccuracy of the standby altimeter is a shortcoming. Other findings included the absence of any information on IMC/IFR procedures in the operator’s manual was also found to be a shortcoming. Consequently a clearance for aircraft operation in IMC is not recommended. Plots of representative engineering data collected in the heavy weapons (configuration 3) and two-tank configurations (configuration 5) are in Appendix D. iv