E-2D Angle of Attack Indexer System Description.pdf

E-2D Angle of Attack Indexer System Description

NAVAIR public release, SPR-2021-762. Distribution Statement A, approved for public release, distribution is unlimited.

Executive Summary The following description of the Angle Of Attack (AOA) indexer system was extracted from NAVAIR 01-E2AAG-1 NATOPS Flight Manual Navy Model E-2D Aircraft. This information was edited to better understand the AOA indexer requirements in the Multi-Engine Training System (METS) performance based specification.

Part Numbers for the E-2D AOA key components are; Approach Indexer MS25317-7, and SmartProbes 123SCAV9776-3. The specification data sheet for the MS25317 Indexer, Approach can be found at: https://quicksearch.dla.mil/qsSearch.aspx

Angle‐of‐Attack System Angle‐of‐Attack (AOA) represents the angle between the longitudinal axis of the aircraft and the relative wind. AOA is calculated independently by each Air Data Computer (ADC). The main components of the AOA system are the SmartProbes, Avionics Flight Management Computers (AFMC), Primary Flight Display (PFD) AOA widgets, and approach indexers.

AOA Measurement Since measurements are made from both sides of the aircraft, the AOA system is able to compensate for angle of sideslip. The benefit is reduced AOA deviations resulting from out of balanced flight conditions. The ADCs send their respective AOA solution to both AFMCs for display on the PFD AOA widget. Selection of ADC 1 or ADC 2 from the Aux DCP determines which data source is providing flight data to the pilot or copilot for display. Heaters are available on each SmartProbe to prevent ice formation and are regulated independently by each ADC.

Control of the heaters is provided by the PITOT switch on the ANTI‐ICING control panel.

AOA Indication An AOA widget is located in the upper left corner of the Attitude Direction Indicator (ADI) grouping on the PFD Primary Flight Reference pages. The AOA graphic is graduated from 0 to 30 units (Figure 2-83). Optimum AOA in the normal landing configurations is 20 units (indicated by a white area at the 3 o’clock position on the graphic). An impending stall is indicated when the pointer is at or above the triangular area. The rudder pedals begin to vibrate at approximately 26 units. The graduations on the dial indicate AOA relative to optimum in units; they do not measure AOA in degrees.

https://quicksearch.dla.mil/qsSearch.aspx

E-2D Angle of Attack Indexer System Description

NAVAIR public release, SPR-2021-762. Distribution Statement A, approved for public release, distribution is unlimited.

A window on the instrument face provides a digital readout of the AOA displayed in units. The digital readout will continue to show accurate AOA, even after the widget has pegged at 30 units, as long as a valid signal is being received by the AFMCs from the ADCs.

The AOA digital readout is normally white text on a black background. When an ADC is degraded, but selected for display on the PFD, this will change to black text on a yellow background.

Selecting the non‐degraded ADC via the Aux DCP will revert the display to white text on a black background if the other ADC is operating normally. When the selected ADC data is unavailable, red x’s will be displayed.

Approach Indexer The AFMCs control the approach indexer on the glare shield above the pilot’s and copilot’s instrument panel (Figure 2-86). The indexer supplements the AOA widget by providing the pilot and copilot with a heads up indication of the aircraft’s AOA. Three lamps shine through cutouts on the face of the indexer in various combinations. When the upper arrow is on, a high AOA is indicated; the lower arrow indicates a low AOA and the circle indicates the optimum AOA. When either arrow and the circle are lit, an intermediate position is indicated. Approach indexer brightness can be varied by rotating the approach indexer rheostat on the center overhead console master. The lights can be checked by pressing the LTS MSTR TEST LSK on the CDU PREFLIGHT page.