decision altitude


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decision altitude (DA)

i. A specified altitude or height in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established. The decision altitude is with reference to mean sea level, whereas the decision height is with reference to the threshold elevation. The required visual reference means that section of the visual aids or of the approach area that should have been in view for a sufficient time for the pilot to be able to assess the aircraft's position and change of position in relation to the desired flight path. In Category III operations, with a decision height the required visual reference is that specified for the particular procedure and operation. For convenience, where both expressions are used they may be written in the form of “decision altitude/height” and abbreviated “DA/H.” These terms replace minimum height (MH), minimum descent (MD), minimum descent altitude/height [MDA (H)], and minimum descent height (MDH).
ii. The height at which a decision must be made, during an ILS (instrument landing system) or PAR (precision approach radar) instrument approach, either to continue the approach or to execute a missed approach.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive ?
As noted in this article's main text, two key changes are highlighted at right: The new, lower decision altitude and the realigned final approach course.
Using the practical definitions, nonprecision minimums are expressed in terms of minimum descent altitude, MDA, and precision approaches have decision altitudes, DAs.
On an approach with a normal glideslope and ILS minimums, the decision bar should appear right over the nose when the aircraft reaches decision altitude.
For example, the FD will guide you accurately down the localizer and glideslope of an ILS or inbound on a GPS approach with or without vertical guidance, but it will not tell you you're flying the proper rate of descent to remain tucked in the FD's notch, or when you have reached an intermediate altitude, decision height, decision altitude or minimum descent altitude.
True, evidence suggests that some "ducking under" decision height, decision altitude or the minimum descent altitude is intentional--the pilot knowingly flies "just a little bit lower" to try to find the runway in the murk.
The study assessed the feasibility of placing the decision altitude (DA) in the Radius to fix (RF) portion of a required Navigation Performance (RNP) approach.
You merely count down the height above the decision altitude from which you'll begin the missed approach procedure.
According to the FAA's Instrument Procedures Handbook, FAA-H-8261-1A, "When a missed approach is executed prior to reaching the MAP (missed approach point), the pilot is required to continue along the final approach course, at an altitude above the DA (decision altitude), DH (decision height), or MDA (minimum descent altitude), until reaching the MAP before making any turns.
OUsing GEOs method of merging RNP to the ILS, operators can experience the track mile reduction benefits of RNP with the lower decision altitudes a precision landing system provides,O said Giovanni Spitale, general manager for GE AviationOs Air Traffic Optimization group.
Altitude corrections should be made to all approach altitudes inside the final approach fix to include decision heights, decision altitudes and minimum decent altitudes (at -35 Celsius with a Height Above Terrain (HAT) of 200 feet, you will have to add 50 feet to your published decision height on the approach plate).