Alert Height and Decision Height

[mach5]

Hello guys , I know the difference between a alert height and a decision height and I thought that the alert height is lower compared to the decision height , but I recently came across a question for wchich the answer was decicion height is lower than alert height .
can any one help me out in this concept.

[skwinty]

This may help.

2.3.1 DECISION HEIGHT DEFINITION
Decision height is the wheel height above the runway elevation by which a go-around must be initiated unless adequate visual reference has been established and the aircraft position and approach path have been assessed as satisfactory to continue the approach and landing in safety (JAA).
2.3.2 ALERT HEIGHT DEFINITION
An Alert Height is a height above the runway, based on the characteristics of the aeroplane and its fail-operational automatic landing system,
above which a Category III approach would be discontinued and a missed approach initiated if a failure occurred in one of the redundant parts of the automatic landing system, or in the relevant ground equipment (ICAO).
In other AH definitions, it is generally stated that if a failure occurred below the Alert
Height, it would be ignored and the approach continued.
Decision height concept:
Decision height is a specified point in space at which a pilot must make an operational decision. The pilot must decide if the visual references adequate to safely continue the approach have been established.
• If the visual references have not been established, a go-around must be executed.
• If the visual references have been established, the approach can be continued. However, the pilot may always decide to execute a go-around if sudden degradations in the visual references or a
sudden flight path deviation occur.
In Category II operations, DH is always limited to 100ft or Obstacle Clearance Height (OCH), whichever is higher. In Category III operations with DH, the DH is lower than 100ft (typically equal to 50ft for a fail-passive automatic landing system and 15-20ft for a fail-operational automatic landing system).
The DH is measured by means of radio-altimeter.
When necessary, the published DH takes into account the terrain profile before runway threshold.
Alert height concept:
Alert height is a height defined for Category III operations with a fail-operational landing system.
• Above AH, a go-around must be initiated if a failure(1) affects the fail-operational landing system.
(1) The list of these failures is mentioned in the AFM.
• Below AH, the approach will be continued(except if AUTOLAND warning is triggered).
The AH is evaluated during aircraft certification; it is set at 100ft for A300, A310,
A319, A320, A321 and 200ft for A330, A340.
The AH is only linked to the probability of failure(s) of the automatic landing system.
Operators are free to select an AH lower than the AH indicated in the AFM but not a higher value. Airbus procedures include both AH and DH concepts for all Fail-operational (see later) Category III operations.

[Denti]

Alert height is aircraft specific and i believe boeing tries to make it 200ft on all its airplanes, it is 200ft on the 737 at least. A higher AH is usually seen as better as it gives a longer time where the automatic system is able to cover failures including loss of ILS signal. 200ft is around the CAT I decision height and we usually dial the CAT I DH in baro and then switch the DH selector to radio with nothing set (no DH 75m RVR). That way we have a mark at 200ft on the altitude band.