Pilots Receive ATC Low Altitude Alert From The Wrong Altimeter Setting

Boldmethod

A student and instructor received a "low altitude alert" from ATC after forgetting to reset their altimeter before an instrument approach. After a long flight, making this simple mistake could leave you hundreds of feet too high or too low on final approach.

Wrong Altimeter Setting

The following NASA ASRS report was published by a CFII giving instruction to an instrument student while flying a Cessna 172...

I was acting as CFII with Instrument ASEL student on training flight, executing the LOC 23L approach at LCK, Glideslope Out. During a previous approach, we received an altimeter setting of 30.21. After the first approach, we re-tuned the ATIS frequency and received new ATIS information at LCK. We confirmed this with Columbus Approach. The student did not reset the altimeter to the LCK setting of 30.16 and I failed to cross-check the student's procedures.

We descended to the MDA at an indicated altitude of 1,220' MSL after passing the FAF, at which point LCK Tower gave a low altitude alert and confirmed that our altimeter setting should've been 30.16. We immediately executed the missed approach procedure. At the time of executing the MAP, we had ground visual contact but did not have the runway in sight.

Boldmethod

Are You Flying Into A Non-Towered Airport?

These pilots were fortunate that they were flying into a towered airport with controllers monitoring their altitude along the approach. ATC was able to issue them a low altitude warning, prompting their immediate missed approach. In this case, the altimeter change was relatively small, but enough to prompt the low altitude warning.

However, if you're flying into a non-towered airport on an instrument approach, center or approach control will switch you over to the airport's CTAF frequency well before you reach DA or MDA. No one will be on-frequency to warn you that you've descended below the minimums for that approach.

Swayne Martin

The Solution? Add A Mental "Trigger" To Your Approach Briefings

Updating your weather information before beginning an approach is critical.

As you brief your approach, use the "frequencies" section of the chart as a mental trigger to ensure you have updated weather information, and announce your updated altimeter setting as you read over the airport's weather frequency.

Boldmethod

These pilots realized their mistake and immediately executed a missed approach, avoiding a potentially larger issue. If you ever find yourself in the same situation, execute the missed approach immediately and set yourself up again.

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