Mattio

If the altimeter setting is missing at an airport and there's no substitute altimeter sources in the comments, you can't do the approach there, right? no options?

rickair7777

Yes, unless it's an emergency. In that case you could use a nearby altimeter setting (from ATIS, ASOS, or ATC) and add an appropriate safety buffer to the MDA.

If you are using an ILS in an emergency you can check the altimeter setting you are using by comparing your indicated altitude at the OM with the published altitude.

AKASHA

According to our Operations Manual, an AWOS is considered out-of-service if the altimeter setting is missing. However, that does not mean we can't fly the approach. We use the current altimeter setting provided by the facility designated on the approach chart. Also, an alternate must be filed that does have the necessary weather reporting.

No emergency required.

Twin Wasp

So you're saying if you're going to MDW and Chicago Approach says the "MDW atimeter is missing, the ORD altimeter is 29.92, descend and maintain 5000" you'd go ahead and later shoot the approach to MDW even though there is no mention of using the ORD altimeter on the MDW plate? Back in my 135 days we had a wavier to use airport's WX ob at a close by airport but we had to go through the NWS to find the variation in altimeter settings over distance and apply a correction. In effect doing what NACA/TERPS does when they publish the ball note for using another airport's altimeter.

AKASHA

Eligible on Demand Operators are provided certain relief from FAR 135.225. Flying an instrument approach to an airport without approved weather reporting (i.e. no altimeter setting) is permitted within certain provisions.

125.225 (b) (2) The latest weather report issued by the weather reporting facility includes a current local altimeter setting for the destination airport. If no local altimeter setting for the destination airport is available, the pilot may use the current altimeter setting provided by the facility designated on the approach chart for the destination airport.

clipperskipper

Sure and you'll also find 135 operators with their own certificated weather observers at various stations, handy when automated services are down/unavailable.

rickair7777

I suspect MDW would be almost identical to ORD.

But the difference between say BUR and PMD could kill you fast.

Of course you can legally do anything with an appropriate waiver.

AKASHA

The facility designated on a BUR approach plate (SoCal App) is different from the facility designated on a PMD approach plate (Joshua App). Therefore, the source of altimeter information would also be different.

Absent an altimeter setting on the field, an Eligible on Demand Operator landing BUR would use an altimeter setting given by SoCal Approach, and landing PMD would use an altimeter setting given by Joshua Approach.

In no case would one use a SoCal altimeter landing PMD. In fact, at least one PMD chart directs you to use Lancaster altimeter in the event PMD altimeter is not available. The BUR/PMD example is misleading.

rickair7777

Nobody who knows the area would ever do that! The point was that airport proximity does not always correlate to similar altimeter settings.

But my original answer stands, the OP did not say anything about being 135, so I answered the question in general part 91 terms. I'm sure we can find an exception to every rule in the book if we look through enough OPSPECs

AKASHA

Nobody in this thread ever made an argument that nearby airports have similar altimeter settings. Quite the opposite. Twin Wasp was suggesting that even airports close to one another could have significantly different altimeter settings (MDW/ORD). So I don't know the point of bringing up BUR/PMD.

I chose not to assume the OP was referring exclusively to 91 operations. He asked if there were any options and I offered an example as it applies to the 135 world. Approval for Eligible on Demand Operations are found in the GOM but not in the OPSPECS section.

Having said all that... now that we're down to splitting hairs... I am curious about the 91 rule. Seems like if you are allowed fo fly a load of paying passengers down an ILS without an altimeter setting on the field, you would be allowed to do the same thing flying solo in your 172. Not saying that's the case because I dont know. Is it another assumption, or are there references to show that it is illegal under 91 to use an altimeter setting provided by the approach controller in lieu of a setting on the field?