HAT Height Above Threshold

[Captain_BH]

Hello ...

For Airbus 320 - usually the FMS profile brings you 50' above threshold... what if you became 150'-200' obove it... heavy.. short runway.. would you pitch the nose down to gain 800 to 900 feet v/s to gain the profile quickly or let it go as it is and if you overrun landing markings would you go around ??

50' above threshold is it a mandatory rule.. where can I find more information about that... Thanks

[firefish]

Most definitely Go Around. And this is not A320-specific but applies to all aircraft/all operations.

In our company we have to be stabilized at 500' agl - otherwise GA. Crossing the threshold at 150', especially when heavy and with a wet runway, hardly qualifies.

I have no idea where the 50' above threshold rule derives from but consider that all performance data (speeds, landing distance etc), regardless of being calculated in the FMS or taken from the paper copy AFM, are based on the aircraft crossing at 50', Vref and on the proper profile and in the proper configuration. By not meeting these criteria you are in effect out of the envelope, maybe too far out, and that can come with a hefty price tag and even with a capital punishment not only for you but for the rest of the crew and the passengers as well.

So yes, I would consider it mandatory. Check your AFM and in the performance section, in this case landing, and it should state how to achieve the speeds and distances supplied by the charts/tables/FMS/... Most likely 50', Vref over threshold, throttles to idle over threshold, etc etc.

[BOAC]

Captain BH - you have been around for at least 4 years here, but your profile tells us nothing. Your posting history questions are slightly odd. Can you fill in some detail as to why you are asking these questions and we may be able to help more. Are we looking at flt sim stuff?

Out of interest, what rate of descent would you consider normal at 150' in a 320? What would you consider to be a maximum?

[TopBunk]

I have no idea where the 50' above threshold rule derives from

firefish

Simplistically, the glideslope antenna is 300 metres from the threshold, which is approximately 1/6th of a nautical mile.

The 3 degree glideslope is about 320 ft/nm, 1/6th of that is about 50ft.

[411A]

I have no idea where the 50' above threshold rule derives from

CAR4B...a long time ago.

[firefish]

I see, thanks.

[rennaps]

Not just an ILS but also in a non-precision approach. ICAO Pans-Ops states:

5.3.2 Determination of the descent gradient for a non-precision approach with FAF

The descent gradient (g) for a non-precision approach with FAF is computed using the equation: g = h/d. The values for h and d are defined as follows:
a) For a straight-in approach use:

d = the horizontal distance from the FAF to the threshold (Cat H, LDAH); and
h = the vertical distance between the altitude/height over the FAF and the elevation 15 m (50 ft) over the threshold.

[stabilized approach]

I was reading across some books for my recurrent study... And this question came to my mind just for curiosity....

What i've read on some books is that the 50' is set for several reasons...
Can be derive from the approach path 3º or any other angle for obstacle , eye reference , energy management...

But mainly it was how all the performance analisys calculations/design were made... Ie. All the landing performance computations are based on the aircraft overflying the TRSHLD at 50' . Sounds obvious to everybody , passing the tshld at 100feet and flying a 3ºGPA would most likely result in touchdown 900' beyond the the 1000'mark and subsequently an increase on total landing distance of 900'(270m).

That's what i've read and looks quite acceptable .