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After an instrument approach in IMC, 91.175(c)(1) requires, among other things, that operations below the DH or MDA must allow for a "normal rate of descent using normal maneuvers."

Can someone point me to a regulation or a definition of what is a normal rate of descent and normal maneuvers under this regulation?

Specifically, my question is whether a forward slip is considered a normal maneuver for purposes of 91.175(c)(1)?

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    $\begingroup$ I think all you really have to go on is the FAA's "unusual attitude" definition: <Pitch attitude greater than 25°, nose up. Pitch attitude greater than 10°, nose down. Bank angle greater than 45°. Within the above parameters, but flying at airspeeds inappropriate for the conditions>. A forward slip that stays within those parameters would meet that requirement I would say, depending on how aggressive it is. For descent rates, what is "normal" depends on your appr speed, but generally, descent rates over 1000 fpm are considered excessive. I don't think you will find any go-no-go limits. $\endgroup$ – John K Nov 1 '20 at 18:10
  • $\begingroup$ @JohnK agreed, to me a forward slip is as normal as using flaps. However, I'm looking for some legal documented backup as it pertains to 91.175(c)(1). I think that definition you described is related to the "upset" AC on UPRT. Probably a good place to start though. $\endgroup$ – Devil07 Nov 1 '20 at 19:01
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    $\begingroup$ Perhaps it would help if you explained the motivation behind the question. $\endgroup$ – Juan Jimenez Nov 3 '20 at 23:40
  • $\begingroup$ @JuanJimenez the motivation is curiosity, but let me give you a scenario. If someone from your local FSDO was watching you pop out from the clouds on an instrument approach and you performed a forward slip to land, would it be a violation of 91.175(c)(1), because a forward slip is not a "normal" maneuver? $\endgroup$ – Devil07 Nov 5 '20 at 4:04
  • $\begingroup$ Its not an easy question. I've spend some time researching it, but thats why I posted it here. I'm going to keep researching it and if I find a definitive legal answer I'll post it. I might have to dig into FAA advisory opinions. $\endgroup$ – Devil07 Nov 5 '20 at 4:06
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I can't find any specific definition of "normal maneuvers", probably because it varies a lot by aircraft type and situation. But I did find AC 120-29A - Criteria for Approval of Category I and Category II Weather Minima for Approach that gives some indication of what the FAA considers not normal (section 4.3.1.6):

Part 91, section 91.175 requires that approach procedures should be based on use of “normal maneuvers” before and after passing DA(H) or MDA(H). Normal maneuvers typically do not involve use of bank angles greater than 30 degrees, pitch attitudes in excess of 25 degrees nose up or 10 degrees nose down, or sink rates in excess of 1100 ft. per minute below 500 ft. HAT while maneuvering to land within the touchdown zone, during go-around, or during a rejected landing. During a missed approach, pitch attitudes in excess of +30 degrees or bank angles greater than 30 degrees would typically be considered excessive.

But even if there is a specific definition of normal maneuvers out there somewhere, I think the context is important too. 91.175 is about instrument approaches, not general flying. So I think you have to ask if slipping to land is a normal maneuver during an instrument approach and I'd say no.

The entire point of an instrument approach is to get you to the runway safely and predictably, and there's a lot of emphasis on stable approaches. I can't think of any obvious reason why you'd need a forward slip if you've flown an approach successfully. You might be able to come up with some scenarios (circling to land? shooting an approach with an MDA of more than 2000' AGL?) however I'm not convinced that it's a normal technique in the specific context of instrument approaches.

If you look at what the FAA says about forward slips in the Airplane Flying Handbook Chapter 8 it strongly suggests that slips are for limited and unusual situations:

Intentional slips are especially useful in forced landings and in situations where obstacles must be cleared during approaches to confined areas. A slip can also be used as an emergency means of rapidly reducing airspeed in situations where wing flaps are inoperative or not installed.

I find it hard to see how those examples fit with executing an instrument approach. But that's just my opinion. If you happen to know a DPE it would be a great question to ask them.

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