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What Makes An Instrument Approach Unstable?

Boldmethod

There's nothing wrong with going around when you're unstable on an approach.

Stabilized Approach Criteria

Unstabilized approaches are one of the leading causes of accidents on landing. So what can you do to make sure you're stabilized as you approach a runway? A quick and easy way to check yourself is with the acronym C-FLAPS:

  • Checklists complete.
  • Flight path (to the runway), proper.
  • Landing configuration, set.
  • Airspeed, within normal approach criteria.
  • Power setting, adjusted.
  • Sink rate, not abnormal.

Follow A 1,000 FPM Descent Rate Limit

The FAA has published guidance on what it considers to be safe descent limits for instrument approaches. Here's what Chapter 4 of the IPH has to say, and what you should know to stay safe on your next IFR flight...

Operational experience and research have shown that a descent rate of greater than approximately 1,000 FPM is unacceptable during the final stages of an approach (below 1,000 feet AGL). This is due to a human perceptual limitation that is independent of the type of airplane or helicopter. Therefore, the operational practices and techniques must ensure that descent rates greater than 1,000 FPM are not permitted in either the instrument or visual portions of an approach and landing operation.

Simply put, sustained descent rates over 1,000 FPM are unstable on approach. Physically, your body cannot perceive and react to descent rates over 1,000 FPM adequately. In the instrument environment with low ceilings and few visual cues, this is especially important.

Live from the Flight Deck

Non-Precision Approaches: When Unstabilized Approaches Lead To Accidents

According to the NTSB and FAA, unstabilized approaches are a key contributor to accidents.

That's especially true with non-precision approaches that have stepdown fixes inside the final approach fix (FAF).

When you're flying a non-precision approach with stepdown fixes, you're required to perform multiple power, pitch, and altitude adjustments, all while flying in the clouds. The real problem is that all of these adjustments increase your workload in a critical phase of flight, and increase your chance for error.

Whether or not your approach has stepdown fixes inside the FAF, using the "dive and drive" method of descending immediately to the approach's minimum altitude can leave you in extended level flight as low as 250 feet above the ground in IMC. When you're that close to the ground and still in the clouds, your chance of something going wrong increases.

Click here to learn how to fly a continuous descent on final approach.

When Should You Go-Around?

At most airlines, continuously exceeding 1,000 FPM on an instrument approach is considered unstable. Momentary deviations are allowed, however. On some aircraft, if there is a "sink rate" aural warning, it can be corrected for by the pilot once. If the warning sounds again, an immediate missed approach must be flown.

In the general aviation world, you're usually flying a slower than an airliner on final approach. Generally speaking, this will keep your descent rate lower as well. If you start to push close to a 1,000 FPM descent rate, you're likely unstable. Consider going around and trying the approach again.

Go-arounds are penalty-free. On the other hand, ignoring a go-around can lead to serious consequences.

What are your go-around criteria on an instrument approach? Tell us in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and a First Officer on the Boeing 757/767 for a Major US Carrier. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), is a former pilot for Mokulele Airlines, and flew Embraer 145s at the beginning of his airline career. Swayne is an author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

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