How precise is the Glideslope antenna?

[Driver 170]

Got me thinking

ILS CAT1 provides certified guidance down to a minimum of 200ft above the runway. Below that, obstacle clearance is not provided even if the aircraft follows the indicated glide slope.

So would we follow the PAPIs after manual flight below 200ft...

[reynoldsno1]

Below that, obstacle clearance is not provided even if the aircraft follows the indicated glide slope.

Not strictly true. An assessment of the VSS (Visual Segment Surface) is also a requirement.

[Driver 170]

It should read above (quote)

Is the VSS part of PANS-OPS?

[aterpster]

Can only speak to TERPs:

The glideslope qualification surface must be clear all the way to the runway. Also, the ILS X, Y, and W surfaces extend from the P-FAF to 200 feet prior to the runway threshold.

[+TSRA]

So would we follow the PAPIs after manual flight below 200ft...

You want to be careful there too as your Eye-Wheel-Height (EWH) may not correspond to the PAPI or VASIS (if used). They're listed here in Canada from P1 to P4 (or V1 to V4 for VASIS) - P1 for something like a Cessna 172, P4 for a B747.

Flying a P4 PAPI in a DH8 will have you above slope, resulting in a longer landing. Flying a P2 PAPI in a B767 will have you below slope, possibly ending up with the wheels touching down before the runway.

I've had way too many FO's contact tower on their own volition, telling them the lights were "out of alignment" only to be told by me on shutdown to look at the airport chart to see what type of PAPI was installed. For many they had no clue there was a grading system and for others they assumed it was always just a 3 degree slope and type didn't matter.

[Chesty Morgan]

Below 200' feet you should be paying attention to everything but the PAPIs and the ILS.

[mishaC172]

Cat IIIb

Doesn't CAT III b antennae type allow landing down to 0 AGL?.. So, probably, precision depends on the type of equipment installed!

[+TSRA]

Doesn't CAT III b antennae type allow landing down to 0 AGL?.. So, probably, precision depends on the type of equipment installed!

Equipment type for ILS CAT II or CAT III doesn't matter for a discussion related to CAT I ILS. Below the minimums you are to conduct the remainder of the approach visually; so even if the equipment has the precision to allow for lower minimums, that's not what you're supposed to be looking at.

[de facto]

So would we follow the PAPIs after manual flight below 200ft.

I certainly do not.

[LookingForAJob]

Doesn't CAT III b antennae type .....

No such thing as a Cat II or III antenna, and the a, b and c bit is a purely aircraft operational matter. In many installations the antennas used for a Cat III ILS are the same as a Cat I, the difference between the two is how much redundancy there is in the white and orange box next to it. If the environment is challenging a more complex antenna array might be necessary in order to provide the stability or precision of the signal that is generated.

[The African Dude]

As others have said, below minimums (200ft on a standard CAT1 ILS) you are VISUAL ONLY. The PAPI do not count. Fly at the runway and land on it without hitting anything else. Your eyes are your guidance.