Weather avoidance on an RNAV arrival

[Paulm1949]

Just wondering what you do for weather avoidance when you’re below MSA on an RNAV arrival or app ? Doesn’t look as easy as if on radar headings ? What are the options ?

[rudestuff]

What do you do for weather avoidance on an ILS below MSA?

[Paulm1949]

So what happens if you’re procedural on an rnav arrival below MSA and there’s a big thunderstorm in the way that you didn’t spot on your scope ?

[Check Airman]

You do the same thing you’d do if you were on a conventional NAV procedure. Asses the risk of flying through the weather vs terrain proximity while off the procedure.

[SloppyJoe]

Think you may be assuming that you have to fly the whole RNAV procedure, this is not correct, it's the same as an ILS, VOR etc. Can be on vectors and then be cleared direct to a point prior to the final approach fix just like being given an intercept heading for an ILS, can ask for headings to get around the weather then ask for direct to a point prior to the faf. Exceptions to this are quite rare, kathmandu for example, where an RNAV procedure is to get in around terrain rather than just a way to get to a runway, in these cases it's assess if you will go-around or land. If the weather is after the final approach fix you should have already made the decision based on the wx radar, just like an ILS, also just like an ILS, if it is after the faf go-around and ask for a heading or fly through it. I assume this is a flight sim question or just a curious enthusiast, if not, ask your instructor or next friendly Captain about it if out of training.

[172_driver]

Climb to MSA and turn away?

[Paulm1949]

I was talking about one of those rnav arrivals below MSA and non radar environment. Say for instance you face a big thunderstorm whilst below MSA but between waypoints that then turned red on the wx radar that wasn’t previously an issue. Can you see the dilemma ? Caught between the 2 waypoints below MSA.

[B2N2]

How far below MSA?

The Minimum Sector Altitude (MSA) is the lowest altitude which may be used which will provide a minimum clearance of 300 m (1 000 ft) above all objects located in the area contained within a sector of a circle of 46 km (25 NM) radius centred on a radio aid to navigation. (ICAO PANS-OPS/I - definitions)

Are you surrounded by terrain a la Quito?
Terrain on one side only like a shoreline airport?
You can’t be that far below MSA otherwise you’d already be close to minimums in which case your question does not apply.

Climb and turn in the direction of the lowest terrain.

[rudestuff]

Originally Posted by Paulm1949

I was talking about one of those rnav arrivals below MSA and non radar environment. Say for instance you face a big thunderstorm whilst below MSA but between waypoints that then turned red on the wx radar that wasn’t previously an issue. Can you see the dilemma ? Caught between the 2 waypoints below MSA.

You do exactly what you would do in IMC on any instrument approach below MSA: You're committed to the approach track so
(a) you push through it and continue
(b) you push through it and go around, climb to MSA then turn, or
(c) you turn below MSA if you're damn sure about terrain.