Innsbruck airfield brief

[Driver 170]

Reading the brief it mentions Flight visibility and ground Visibility? Can someone explain the difference please. I gather ground vis is basically what’s reported on the METAR.

[eckhard]

Flight visibility is generally defined as “the forward visibility from an aircraft in flight”.

As a result, it’s normally only the operating crew who can decide what their flight visibility actually is.

Ground or “Met vis” (Meterological visibility) is normally measured by a competent observer (can be ATC or a Met person) by seeing which landmarks are visible from the tower. Certain buildings, hills, even conspicuous trees will have had their distances accurately measured and the observer will ascertain which of these are visible at the time of observation.

For Runway Visual Range (RVR), this is now measured automatically by transmissometers and is normally only reported when the RVR is less than 1500m.

[Driver 170]

So, how can I calculate my forward visibility for flight if i’m on the ground? Pilot reports maybe?

[eckhard]

From the LIDO entry for INN:

“In the area around INNSBRUCK it may happen that different values of VIS exist in various directions mainly caused by a haze or mist layer over the city. If such situations are observed and the ground VIS is 8km or less, an additional reference in plain language to the INNSBRUCK MET REPORT is made or ATC will refer to. This plain-language-appendix refers especially to an existing haze layer and as far as
possible to the estimated VIS above this haze layer.”

So yes; I suppose “as far as possible” means they will use Pireps and other local procedures (observations from the mountains?)

In the mid-1990s I used to fly 737-400s to Innsbruck most winter weekends. I don’t remember having to worry too much about in-flight visibility. Provided that the Met reports were above minima, we would make an approach and land. I remember that the in-flight vis had to be assessed at certain points, inasmuch as one had to be able to see a church spire or some such at a certain DME. My memories are that the visibility was normally very good. The only times I diverted were from holding altitude because the weather was clearly below limits and there was no point in attempting an approach.

This was getting on for 25 years ago, so maybe someone with more recent experience can provide more information?

[Driver 170]

This is from brief

3. SPECIAL CONSIDERATIONS 3.1 WEATHER

Cloud base is usually greater than 3,000ft during winter. During snow/rain showers visibility and cloud base may be lower. On average only 5 days per month have visibility below 800m. Fog possible during early morning when ground is snow covered.
When snow/rain showers are forecast they generally pass within 30 minutes. Wind is predominantly from west unless Foehn wind is present.
A local phenomenon exists known as the ‘Stadtwuzl’ which literally means ‘dust ball’, but is used here to describe the ‘fluffy’ cloud that often sits over the city of Innsbruck in the early morning. It sits at a height of 300 – 800ft AAL and its presence is indicated in the METAR as FEW 005 (or SCT) BKN 011. It sits below other cloud and obscures the runway when approached from the East. It may appear as a remark in the METAR: ‘Low Cloud in FNA’ (FNA = Final Approach).
Weather reports are available from Innsbruck Volmet (130.475). Innsbruck Volmet can be received in the area of Belgium – listen early. The following locations are available:

1. Patscherkofel (7,371ft) – 5 nm SE of Innsbruck on east side of Brenner pass.
2. Absam (AB)/Rinn – Reported if cloudbase 5,000ft aal or below
3. Visibility in various directions if observed

Item 2 is useful for the first and second decision points for the LOC DME WEST procedure
.
Item 3 is reported when there is a haze or mist layer over the city. In this case the actual visibility and the estimated visibility above the haze are reported. In these conditions ATC may recommend RWY 08 for landing due to visibility over the city (final approach for RWY 26).