So, I was watching a video of a Boeing 737 NG land, and heard the "5" callout. Is that an airline option or something?
EDIT : link to video
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$\begingroup$ I would be willing to bet that it's related to this question/answer, which says that if they maintain the same altitude (probably during the flare in this case) for more than four seconds, it will make a new announcement with the current altitude: aviation.stackexchange.com/a/47098/69. The airplane that I fly has a 10' callout, but on a couple of occasions over the six years that I've flown it, I've heard it call out 5', and thought that it was odd (I probably floated longer than normal and didn't realize that was the cause!). $\endgroup$– LnafzigerNov 5 '19 at 16:03
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$\begingroup$ Thanks for sharing the video link :) @Lnafziger in the video the callouts "50, 30, 20, 10, 5" all come very close together, so it cannot be related to that. I have also never read anything like that in a Boeing manual. $\endgroup$– BianfableNov 6 '19 at 18:49
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The Rockwell Collins EGPWS, that is probably the most widely used system (you can tell right away by the voice that sounds exactly like the character "Data" from Star Trek - Next Generation; I'd swear it's the same actor's voice) comes with the full range of callout altitudes/heights and airlines pick and choose which ones they want by "configuration strapping" settings (connector pin jumper configurations in the mounting tray) when the units are installed in the avionics bay.
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$\begingroup$ Fo you have a link to the configuration mechanism? I've never heard of such mechanism and would like to learn more. $\endgroup$– Manu HNov 5 '19 at 14:48
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1$\begingroup$ On older avionics there would be physical jumper hardware at the connector that provides on-off inputs or DIP switches on the back of the avionics unit. On modern ARINC 429 avionics there is usually what is called a Configuration Strapping Unit (CSU) avionicsales.com/product/… which is a module full of DIP switches that do the "jumper" function (basically a mode on or off signal) for the various on-wing setup options. Do some rummaging around on the web for CSU and you'll probably stumble onto some training material. $\endgroup$– John KNov 5 '19 at 17:52
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$\begingroup$ Configuration using DIP switches and hardware jumpers? What is this, 1992??? Oh, yeah, aviation... technology move slowly in the aviation industry - that is probably the latest update flying. $\endgroup$– FreeManNov 6 '19 at 14:10
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$\begingroup$ Don't know for sure, but on the latest avionics suites like Proline Fusion I'm pretty sure it's done by software. $\endgroup$– John KNov 6 '19 at 19:43
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Yes, that must be an airline option. My Boeing 737 NG FCOMv2 says (15.20.17 Warning Systems - System Description):
Approach Callouts
Radio Altitude Callouts
The GPWS provides the following altitude callouts during approach:
- 2,500 feet – TWENTY FIVE HUNDRED
- 1,000 feet – ONE THOUSAND
- 500 feet – FIVE HUNDRED
- 100 feet – ONE HUNDRED
- 50 feet – FIFTY
- 40 feet – FORTY
- 30 feet – THIRTY
- 20 feet – TWENTY
- 10 feet – TEN.
Note: Callouts at 1000 feet and 500 feet are based on barometric altitude above the landing field elevation; callouts at 2,500 feet, and below 500 feet are based on radio altitude.
The FIVE callout is not listed here and I actually never heard it (could you link the video?). But since not all airlines have all of these callouts, it must be an airline option.
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1$\begingroup$ Any idea why they switch from radio to barometric then again to radio? I'd have expected it to be barometric above a certain altitude then radio all the way down $\endgroup$ Nov 5 '19 at 11:41
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3$\begingroup$ @DeepSpace The 2500 feet callout is where the RA comes alive (it is also not displayed on the PFD before). It also warns you that you are now close to terrain (it is part of the Ground Proximity Warning System after all). The following callouts are barometric because above uneven terrain, this would not be very helpful in determining time until touchdown (1000 and 500ft are usually the altitudes at which you have to be stabilized in VMC and IMC respectively). The rest is RA again because now you are very close to the runway and more accuracy is needed. $\endgroup$ Nov 5 '19 at 11:46
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2$\begingroup$ I think you mean, stable at 1,000 in IMC and 500 in VMC, yes? $\endgroup$– Ralph JNov 5 '19 at 15:59
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$\begingroup$ @RalphJ Oops, yes you're right of course, I mixed that order up. $\endgroup$ Nov 5 '19 at 16:02
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