HiPerhaps someone may know why on PIC you can set the decision height only in multiples of 10 and also to a minimum of 0 ie why no negative numbers?Any ideas?

>why no negative numbers? Not sure, but I had always assumed that DH was measured in feet AGL?Ian Elchitz CYWG

I would be worried if put NEGATIVE numbers in the DA. No one would like to put a dent in the runway before deciding to GA(way too late for that). Yes DA is measure in AGL.Pluto1168(kelvin)

When NOT planning to do an autoland you are meant to reduce the DH is something below 0 so DH becomes invalid. Effectively your DH then becomes your minima, and that depends on what sort of approach you are doing eg ILS/DME, LLZ etc.

Hi, Tom.I believe the PIC team are aware of this anomaly... and I feel confident that they will correct it in their next simulation whatever that may be ;-)According to my company training notes on the DH panel, the range of altitudes available is 999' to minus 20'. However, the DH alerting system is linked to the Radio Altimeters only, which generally only registers positive values for height. The only way you would see a negative Rad Alt value before touchdown is if you were landing with the gear up and/or with no flare angle!Actually, there is another, more unlikely scenario: Each Radio Altimeter system is composed of a transceiver (i.e. a transmitter-receiver), a transmit antenna(underneath the fuselage), a receive antenna (slightly behind the transmit antenna) and coaxial cables running between the antennae and the transceiver. Radio Altimetry is based on measuring how long a microwave radio signal takes to go from the transceiver, to the antenna, to the ground, back to the (receive) antenna and then back to the transceiver. The same model transceivers can be fitted to a variety of different aircraft, which, as you can imagine, may have different flare angles, different gear configurations, different cable lengths, etc. Because of this there must be some sort of compensation made inside the transceiver so that the altimeters of these different aircraft all read 0' on touchdown. There are various time delay circuits inside the transceiver to allow for this. Selection of a particular time delay circuit is made by shorting out electrical pins on the back of the transceiver. This allows the transceiver to compute the correct height for your particular aircraft. However, if the wrong pins had been shorted out on your aircraft, the radio altimeter may read 0 or a negative value before touchdown. This is very unlikely however.Anyway, hope this helps.Cheers.Ian.

Hello Tim,I don't understand what you mean, :-( ? Surely, Decision Height has to be a positive value above ground level, the point at which the pilot must continue the landing or perform a Go Around?It would have made more sense to me if you had said that DH is invalid when you ARE doing an autoland, since the aircraft is being guided by the AP, and decision height is irrelevant(?)By the way, am I correct in thinking that DH only applies to ILS approaches(otherwise MDA)? Is DH therefore always equivalent to MAP? Clear up my confusion, please!Thanks,Frank

Hi Frank DH only applies to autolands!

Hi IanI must admit after the 2nd paragraph you kinda lost me but I get the jist of what you are trying to say.It's just that I have been very reliably informed that by changing the DH to a negative number it kinda invalids it, which leaves minima which you bug :-)This is true for BA, maybe it is company specific - especially as PIC is modelled on an AAL 767?

For all CAT I operations we set the DH selector to 200'For all CAT II/III ops we set the DH selector to the DH.Our aircraft dont give us the "minimums" callout, so we dont get an annoying callout at 200' even tho this isn't the DA.For aircraft that do this, just set a negative value for the DH and it wont disturb you.Remember that even in autoland situations you may well have a DH (which may be company imposed), thus the DH selector is critical for autoland approaches.When not flying a CATII/III approach you are using a DA, not a DH, hence why you set the DA (an altitude) on the altimiter for CATI and above. And you set the DH (a height) on the radio altimiter for CATII/III.

In PIC however, what would set the DH to if you wanted to do a normal CAT3B autoland? 10 or 20?

Hi Tim,"DECISION ALTITUDE/DECISION HEIGHT [iCAO]- A specified altitude or height (A/H) 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." (from Pilot/Controller Glossary at http://www.faa.gov/atpubs/PCG/)My understanding is that DH applies to precision approaches per se, and is not confined to autolands? MDA is used for non-precision approaches.Anyone else care to comment?Best wishes,Frank

Hi Tom,Apologies for getting your name wrong, twice! :-(/Frank

LOL np :-)

DH-Cat II/III ILS.DA-Cat I ILS.MDA-Any VOR/NDB/DME/GPS approch.

To whatever the minima on the chart is :-)