Beeping alarm during landing

[spiffyone]

Welcome, Captain Hutch. This is actually spiffytoo, husband of spiffyone. I'm using her computer and am too lazy to find my password. :)

I thought I would ask you about a flight I had a few years ago on the now-defunct Midway Airlines. I took a flight from Raleigh to Columbia on a very tiny plane, about 15 seats. If Wikipedia is correct, it was a Jetstream 31:

http://en.wikipedia.org/wiki/Jetstream_31

There was no partition between the passengers and pilots, so we could see and hear everything that was happening. They warned us that it would be a rough ride (it was about 100 degrees that day), and the plane was buffeted quite a bit by turbulence. Unlike in a larger plane, it would rotate in all three axes at once when it hit a bump, which took some getting used to.

Then we came in to land, and either as we hit the runway, or just before (I can't exactly remember), this loud beeping alarm went off. The pilots didn't seem too concerned, and one of them just reached up and turned it off. Of course we landed without incident. What might this have been?

[cshollingsworth]

I bet it was their alarm clock telling them it was time to wake up and land the plane. :lol:

Just kidding, but I would have been freaking out if I heard an alarm bell on landing (or at any other time during a flight actually). Hope the captain answers your question soon...I'm curious too!

[spleisher]

It is not uncommon at all for the stall warning horn to go off just before touch-down on a landing. If it was a really obnoxious buzzing noise, I'll betcha that's what it was.

Remember, when you flare before landing, you're basically bleeding off the last bit of airspeed the plane needs to fly. If you do it just right, the airplane will be right at a stall just as you reach the altitude of the runway. In that case, the stall warning horn can go off for just a second before the plane settles on the runway. If it's going off much higher than a few feet off the groud, that's not a good thing. Also, keep in mind that just because the stall warning is going off does not mean the wing is stalled. The warning horn will sound a few knots above the stall speed, signaling an impending stall.

Anyway, Captain Hutch can provide more detail or correct my theory, but that's my best guess.

[mkahanek]

Auto-Pilot disengaging. On commercial jobs when a pilot disengages the auto-pilot there is a very audible alarm alerting them to the fact. On Continental it is three loud buzzes. This feature was put in place after an accident which was caused by the auto-pilot disengaging and the pilots not knowing it. Now commercial aircraft will bitch pretty loudly when "otto" is disengaged.

[Captain Hutch]

Spiffyone/too,

I tend to go with Mkahanek on the beeping sound. First of all, I am not familiar with the Jetstream 31, so I can only come up with an educated guess. On the versions of 737’s that I fly, when the pilot disconnects the autopilot there is a loud intermittent horn that goes off and to cancel the horn either pilot must hit the disconnect switch again. However this switch is right next to the pilot’s thumb so most of the time there is a very short time that the horn will sound. It is hard for me to imagine a switch that the pilot would have to “reach up for” to cancel a horn with the airplane so close to landing. On almost all flights we will switch over from the autopilot to manual flying somewhere before landing—it might be several seconds to ten or fifteen minutes depending on the pilot and the weather conditions. On flights where we use the autoland function, which practically is not too much of the time, since the weather would be fairly foggy and the runway avionics must be equipped to handle the autoland function, the pilot will disengage the autopilot after the nose wheel touches down. Also, I would guess that the passengers in the first or second row of the aircraft would be able to hear this warning horn even through the cockpit door.

Another factor to remember is that most aircraft are designed so that any warning horn that can be cancelled by pushing a switch is usually not that important. For instance, a warning horn will sound if the landing gear is not down (heaven forbid!) and the rest of the airplane is in the landing configuration. The pilot cannot cancel this warning horn.

Hope this helps. :tiphat:

Hutch

[spiffytoo]

I never would have thought of the autopilot. Thanks to those who responded.

Also, please don't take too literally my comment about the pilot "reaching up" to turn the alarm off. I honestly don't remember exactly where the switch was.