Local altimeter setting required?

[jrh]

Here's a deep dive one of my coworkers questioned me on and I'd like to hear how others handle it, particularly under Part 135...

Scenario is an untowered airport that normally has automated weather, but the automated weather is inop. Multiple approaches are published, including ILS, GPS, and VOR. None of the approaches mention anything about an altimeter setting in the notes section except for a single GPS approach that includes a note saying, "When local altimeter not received, use XYZ altimeter setting," referring to a nearby airport.

Does this mean this is the only approach authorized for use in this scenario?

AIM 5-4-5 says, in part, "When the altimeter setting(s) on which the approach is based is not available, the approach is not authorized."

Part 135.225(b)(2), referring to eligible on-demand operations, says an approach may be conducted "...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."

So basically, my questions are:

What determines if an approach gets a note referring to a remote altimeter setting source? I found the exact formulas and standards for a RASS in FAA Order 8260.3F, but no guidance on when exactly a RASS will be developed for an approach.

Is there a difference between Part 91 operations and Part 135 eligible on-demand operations? The AIM seems to indicate this is a black and white no-go issue, but the wording of 135.225 seems to say whatever altimeter setting ATC gives for the area is an acceptable substitute.

How would a note stating "When local altimeter not received, procedure NA," play in to all of this? According to the AIM, that statement is redundant. Or is it there in order to explicitly prohibit eligible on-demand operators from using the approach when no weather is available?

 

[Roger Roger]

I have always understood it as a hard no go. 2 airports we go to 27 NM apart, airport A approach has a note that you can use airport B altimeter if airport A not available. But airport B approaches do not have an equivalent note. I think whether an approach gets alternative altimeter settings is just down to whether the approach designer felt like it that day and whether someone has requested it.

 

[jrh]

I have always understood it as a hard no go.

My follow-up question then becomes, if this scenario is a hard no go, what scenario is 135.225(b)(2) written for then?

I was trying to think of a plausible situation and couldn't come up with anything else, but maybe I'm not creative enough.

 

[Roger Roger]

My follow-up question then becomes, if this scenario is a hard no go, what scenario is 135.225(b)(2) written for then?

I was trying to think of a plausible situation and couldn't come up with anything else, but maybe I'm not creative enough.

I think by “facility designated on the approach chart” it just means the applicable AWOS or ATIS designated as an approved alternate, and with the modified minima listed. Without that clause, the letter of the law would prevent 135 on demand operators from using an alternative altimeter setting listed on the chart because it’s not a “local altimeter setting for the destination airport”.

ATC can give you whatever altimeter you ask for but that doesn’t mean you’re authorized to use it. at least that’s the way we all interpreted it when it came up in our operation.

 

[jrh]

I think by “facility designated on the approach chart” it just means the applicable AWOS or ATIS designated as an approved alternate, and with the modified minima listed. Without that clause, the letter of the law would prevent 135 on demand operators from using an alternative altimeter setting listed on the chart because it’s not a “local altimeter setting for the destination airport”.

ATC can give you whatever altimeter you ask for but that doesn’t mean you’re authorized to use it. at least that’s the way we all interpreted it when it came up in our operation.

Gotcha, that makes more sense. I was reading "facility" to mean "ATC facility" but I see how it means "weather reporting facility."

I continued diving through the interwebs tonight and found FAA Order 8260.19J breaks down and spells out exactly when to use the various notes, such as when local altimeter not received, use XYZ altimeter, or procedure not authorized, or whatever the case may be.

For what it's worth, in your example above about the two airports without reciprocal notes, I think it relates to the various levels of automated weather available, if they are tied in to the weather distribution network, etc. At least that's what my reading of 8260.19J leads me to believe. One airport probably has a more advanced weather system than the other.

It's funny to me how I can go so long without even thinking about this stuff, then one question sends me down a rabbit hole of regs, FAA orders, letters of interpretation, and more. In the end it all circles back to being quite simple. Get the local altimeter, or whatever altimeter the chart calls for, otherwise you can't go.

 

[DE727UPS]

A thought I had about AIM vs part 135 is AIM is non-regulatory and part 135 is. I'd defer to part 135 if you perceive a difference in the language between the two. Secondly, never heard of part 91 on demand. I always thought that meant 135 but don't think it's really an FAA term but more of an industry thing.

 

[jrh]

A thought I had about AIM vs part 135 is AIM is non-regulatory and part 135 is. I'd defer to part 135 if you perceive a difference in the language between the two. Secondly, never heard of part 91 on demand. I always thought that meant 135 but don't think it's really an FAA term but more of an industry thing.

I thought about the non-regulatory nature of the AIM, but after more studying I've realized the discrepancy was really only in my head.

"Eligible on-demand" is a term from Part 135.4. If an operator has the OpSpec and meets the criteria listed in 135.4, it allows them to operate out of airports without weather reports (not normally allowed under Part 135) and land jets on shorter runways than other 135 operators who don't meet the criteria. It's basically a must-have OpSpec for any operator wanting to serve small, out of the way towns.

The thing in this case is that it leads to some weird scenarios. When a 135 pilot hears the weather reporting station is inop, first thing they think is "No big deal, we are eligible on-demand." Except it is a big deal if there's no altimeter source to fly the approach.

Airports without weather reports will have approaches designed to use altimeters from other locations. Airports WITH weather don't have approaches designed with a lack of weather in mind. Take Grand Junction, CO (KGJT) as an example. If the weather goes offline there, every single approach becomes not authorized.

 

[Roger Roger]

I thought about the non-regulatory nature of the AIM, but after more studying I've realized the discrepancy was really only in my head.

"Eligible on-demand" is a term from Part 135.4. If an operator has the OpSpec and meets the criteria listed in 135.4, it allows them to operate out of airports without weather reports (not normally allowed under Part 135) and land jets on shorter runways than other 135 operators who don't meet the criteria. It's basically a must-have OpSpec for any operator wanting to serve small, out of the way towns.

The thing in this case is that it leads to some weird scenarios. When a 135 pilot hears the weather reporting station is inop, first thing they think is "No big deal, we are eligible on-demand." Except it is a big deal if there's no altimeter source to fly the approach.

Airports without weather reports will have approaches designed to use altimeters from other locations. Airports WITH weather don't have approaches designed with a lack of weather in mind. Take Grand Junction, CO (KGJT) as an example. If the weather goes offline there, every single approach becomes not authorized.

Since visual and contact approaches are IFR procedures, do you need a local altimeter setting for them? My first instinct says yes, which means even in good wx in a turbojet you need to get within 10 miles and cancel IFR.

 

[jrh]

Since visual and contact approaches are IFR procedures, do you need a local altimeter setting for them? My first instinct says yes, which means even in good wx in a turbojet you need to get within 10 miles and cancel IFR.

I'd say no for a few reasons.

The AIM 5-4-5 reference I quoted above is specifically in relation to instrument approach charts. Obviously visual and contact approaches don't have charts.

135.225 specifically refers to instrument approach procedures, which are defined in Part 1.1 as "...a series of predetermined maneuvers by reference to flight instruments with specified protection from obstacles and assurance of navigation signal reception capability..." aka a traditional approach, not a visual or contact.

From a common sense perspective, visual and contact approaches are visual maneuvers 100% of the time, even though the aircraft is on an IFR clearance still. Altimeter setting is pretty much irrelevant when the goal is to use visual cues to not hit stuff. This is the opposite of an approach with minimum altitudes at various points.