4 digital "chirps" before landing: what do they mean?
Dec 25, 2017, 3:43 pm
#1
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4 digital "chirps" before landing: what do they mean?
Nit-picky technical aviation question:
When a plane is about to land, I often hear 4 digital "chirps": four sort of high-pitched digital "beeps". They usually come a few minutes before touchdown.
What do they mean, and what makes the noise?
Thanks!
When a plane is about to land, I often hear 4 digital "chirps": four sort of high-pitched digital "beeps". They usually come a few minutes before touchdown.
What do they mean, and what makes the noise?
Thanks!
Dec 25, 2017, 3:55 pm
#2
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Likely the middle or inner marker. These are radio beacons on the approach course and used to mark decision points on the approach. They appear as both audio (tones) and visual (panel lights) for the pilots.
Dec 25, 2017, 4:20 pm
#3
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Is this over the PA, or from the cockpit, or somewhere else? Is this specific to an airline? Or a specific aircraft type?
I doubt it would be the middle or inner markers if they are "a few minutes" before landing. The middle marker indicates the decision point on an ILS to go missed if the runway environment is not in sight (on most ILS approaches this is 200 feet above ground, or maybe 20-ish seconds before landing). The inner marker indicates the aircraft is over the threshold, so this obviously wouldn't be it. Maybe it's the outer marker (indicates glideslope intercept location, which would be a few minutes before landing). The Wikipedia page has audio examples of each.
It could just be an indication from the pilots to the FAs to finish their inflight duties and get buckled in.
I doubt it would be the middle or inner markers if they are "a few minutes" before landing. The middle marker indicates the decision point on an ILS to go missed if the runway environment is not in sight (on most ILS approaches this is 200 feet above ground, or maybe 20-ish seconds before landing). The inner marker indicates the aircraft is over the threshold, so this obviously wouldn't be it. Maybe it's the outer marker (indicates glideslope intercept location, which would be a few minutes before landing). The Wikipedia page has audio examples of each.
It could just be an indication from the pilots to the FAs to finish their inflight duties and get buckled in.
Dec 25, 2017, 5:31 pm
#4
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from my long-ago Boeing Flight Test experience, I’m pretty sure those four chirps are indeed the MM ... they’re clearly coming thru the flight deck speakers, and they’re generally audible in the first few rows of the cabin
Dec 25, 2017, 5:35 pm
#5
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I think you're probably hearing the autopilot disconnect warning. You can hear it from a 320 on the following video starting at 0:09.
Most MM and OM are going away. Even where they still do exist, they aren't likely to be played on a speaker.
Most MM and OM are going away. Even where they still do exist, they aren't likely to be played on a speaker.
Dec 26, 2017, 10:11 am
#7
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I most recently heard it on a CRJ 700 or CRJ 900 (forget which) but also hear it on Airbus planes. I don't think that it's over the intercom. Thanks, everyone--this is very helpful feedback.