Honking horn sound

[kevinh 409]

I would love to hear the logic on that whole fiasco.

It dates from the days of the original 737 with a basic electro-mechanical aural warning unit. Unless the air sensing logic fails the takeoff config warning can only occur on ground so doesn't conflict with a cabin altitude alert. So there should be no confusion, in theory.

[Spin737 102]

It dates from the days of the original 737 with a basic electro-mechanical aural warning unit. Unless the air sensing logic fails the takeoff config warning can only occur on ground so doesn't conflict with a cabin altitude alert. So there should be no confusion, in theory.

In theory. Tell that to Hans-Jürgen Merten from Helios 522. He thought it was the take-off config horn. I'm heading in to the sim on Sunday and I think one of the problems we'll deal with at some point is a air/ground fault. Config horn blaring at you until you can figure out a solution. I don't think it involves the O2 mask.

 

It would make more sense to have the Landing Config horn and the Takeoff Config horn the same and the Cabin Alt different.

[kevinh 409]

In theory. Tell that to Hans-Jürgen Merten from Helios 522. He thought it was the take-off config horn. I'm heading in to the sim on Sunday and I think one of the problems we'll deal with at some point is a air/ground fault. Config horn blaring at you until you can figure out a solution. I don't think it involves the O2 mask.

 

It would make more sense to have the Landing Config horn and the Takeoff Config horn the same and the Cabin Alt different.

Indeed. Logically the crew should think "we're in flight, it's most likely to be a cabin altitude problem". Logic goes out the window with that deafening horn going of course. Even so, if it is a cabin altitude problem you can cancel it using the overhead horn cutout button. If it's TO config warning it can't be cancelled unless you set a TO config or reduce thrust lever position.

 

I would have though your first action should be to try and cancel the horn. If it won't cancel then it's a config warning problem, otherwise work on the cabin pressure issue.

[downscc 1,327]

For a moment I recall and then miss ######ing Betty from the MD-11.

[Spin737 102]

Indeed. Logically the crew should think "we're in flight, it's most likely to be a cabin altitude problem". Logic goes out the window with that deafening horn going of course. Even so, if it is a cabin altitude problem you can cancel it using the overhead horn cutout button. If it's TO config warning it can't be cancelled unless you set a TO config or reduce thrust lever position.

 

I would have though your first action should be to try and cancel the horn. If it won't cancel then it's a config warning problem, otherwise work on the cabin pressure issue.

I'd rather not have to figure out which warning it is. One for Cabin Alt and a different one for the configs.

[JoeDiamond 67]

 

 

I'd rather not have to figure out which warning it is. One for Cabin Alt and a different one for the configs.

 

At least now you have a light to tell you which one it is.

[kevinh 409]

I'd rather not have to figure out which warning it is. One for Cabin Alt and a different one for the configs.

Pushing the horn cutout switch is that difficult? Boeing in their wisdom decided it was important to keep the same aural warnings to minimise differences between versions. It was exactly the same aural warning logic on the 727 and 747 Classic. Keeping the legacy design was probably a big mistake. They should have gone for a new layout and modernisation along the lines they did with the 747-400 and McDD did with the MD-95. They would still have retained the same type certificate.

 

The real problem in the Helios accident was that the crew did not consider the possible alternative, even when the cabin oxygen deployed. They were fixated on it being a configuration warning. However by then hypoxia had taken hold.

 

However since Helios a mod has been available to install warning lights which identify the reason for the intermittent horn. Don't Alaska Airlines have this mod?

 

http://www.b737.org.uk/pressurisation.htm, search for "Cabin Altitude Warning" (about two thirds of the way down the page.

[Spin737 102]

 

 

At least now you have a light to tell you which one it is.

 

However since Helios a mod has been available to install warning lights which identify the reason for the intermittent horn. Don't Alaska Airlines have this mod?

 

Some of the planes do. Alaska has -4, -7, -8, and -9. I think only the later -8s and -9s have them and some of them came from Boeing installed incorrectly and are placarded inop. We still read AD2008-23-07 every day and won't stop until the entire fleet is fitted with the lights.

[downscc 1,327]

I find this interesting... a typical general aviation pressurized aircraft has a light but no audible per FAA certification requirements.  At least the ones I'm familiar with.  Of course, a C-414 takes much longer to climb through 10,000 LOL.

[JoeDiamond 67]

 

 

I find this interesting... a typical general aviation pressurized aircraft has a light but no audible per FAA certification requirements. At least the ones I'm familiar with. Of course, a C-414 takes much longer to climb through 10,000 LOL.

 

I suspect that has to do with the service ceiling being lower on the GA aircraft.  The time of useful consciousness at FL410 is a lot shorter than at FL250.  Without the audible warning you wouldn't stand a chance if you had a rapid depressurization at the higher altitudes.

[downscc 1,327]

I suspect that has to do with the service ceiling being lower on the GA aircraft.  The time of useful consciousness at FL410 is a lot shorter than at FL250.  Without the audible warning you wouldn't stand a chance if you had a rapid depressurization at the higher altitudes.

That makes a lot of sense.  I lost pressure at FL230 and the Chancellor is not a dive bomber, it took forever to get below FL190 where I started feeling better about the outcome.  That was  interesting... yeah, the masks were in a bag somewhere.  I do remember the physiological sensations, mild ear clearing, but not the light; so yes, a horn is a good idea.  We had an altitude chamber at Offutt AFB back in my time there....that is something I recommend to anyone who has the access. Oh yes, I remember calling in my immediate descent to Memphis Center who was real quick at clearing me lower but I was already gone (as the song says).