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PPRuNe Forums (https://www.pprune.org/)
-   Accidents and Close Calls (https://www.pprune.org/accidents-close-calls-139/)
-   -   SWA 737 overrun at BUR - Dec 6 2018 (https://www.pprune.org/accidents-close-calls/616111-swa-737-overrun-bur-dec-6-2018-a.html)

ManaAdaSystem 14th Dec 2018 21:25
Yes, I see that, but I said this with reference to the short and icy runway discussion.
Most of the time I’m not landing weight limited, so no need to go below the GS.

172_driver 14th Dec 2018 21:57
On my plane if the radar altimeter crosses the threshold at 50ft, the landing gear crosses at 22', so dipping 20 feet low and I will hit the runway edge lights. Don't flare long or reduce power too late.
The 737 radio altimeter reads 0 at touch down - i.e. distance between my sole and ground. I would have thought the same applied over the approach lights with slight variance for different deck angles, perhaps?

73qanda 14th Dec 2018 22:09
Only one foot variance.
Not sure what your ‘sole’ is but the gear is 15ft lower than your eyes when you are sitting in your seat with either flap 30 and 2.4 degree body angle or flap 40 and 1.4 degrees body angle.

172_driver 14th Dec 2018 23:23
I meant bottom of my boots - i.e. my gear. When the "fifty" is called doesn't that mean my gear is 50 ft off the ground? Me sitting 15 ft higher is then 65ish ft up in the air.

I am not saying I have the answer - but I think the radio altimeter is calibrated to read distance between the wheels and the ground. Thus I am not going to drag my wheels through the approach light for being "a tad low on my RA",

PJ2 15th Dec 2018 00:26
I meant bottom of my boots - i.e. my gear. When the "fifty" is called doesn't that mean my gear is 50 ft off the ground? Me sitting 15 ft higher is then 65ish ft up in the air.
I don't think so...

https://cimg6.ibsrv.net/gimg/pprune....133ecca2d2.jpg

Also, 737 radio altimeters do not usually read '0' on the ground. The readings I've seen (in data) are in the -4 to -2 range.

The radio altimeter antennae are located just behind the EE-bay access door. The #2 RA Transmitter is first, then the #2 RA receiver, then the #1's in the same order.

73qanda 15th Dec 2018 00:29
When the "fifty" is called doesn't that mean my gear is 50 ft off the ground? Me sitting 15 ft higher is then 65ish ft up in the air.
On a standard ILS with a 50 ft TCH, the ILS antenna will cross the threshold at 50ft. The ILS antenna is about 3 feet in front of your chest and 15ft above the gear. The “fifty” call seems coincident with crossing the threshold in my experience.

Capn Bloggs 15th Dec 2018 00:56
172's question was related to the rad alt call, not the ILS TCH. Why would the rad alt call "50" if the wheels were only 35ft off the ground? In my jet (not 737), when it calls "5", I'm still in the air...

PJ2 15th Dec 2018 01:50
RA calls are generated by the GPWC and may be pin-selectable (on/off). So far, the AMM isn't clear on the how the call is generated.

73qanda 15th Dec 2018 02:03
Fair point.
I guess my question would be “ Does the rad alt call “fifty” when the rad alt is 50ft above ground? or does that rad alt call “ fifty”when the gear is 50ft above the ground?. I don’t think it calls it when the gear is at 50ft because it so often appears to call it exactly when we cross the threshold.

737er 15th Dec 2018 02:32
Originally Posted by PJ2 (Post 10335996)

Also, 737 radio altimeters do not usually read '0' on the ground. The readings I've seen (in data) are in the -4 to -2 range.
If you look, it’s always at 0 at wheel touch. The -2 is after strut compression.

hans brinker 15th Dec 2018 02:41
Originally Posted by 73qanda (Post 10336019)
Fair point.
I guess my question would be “ Does the rad alt call “fifty” when the rad alt is 50ft above ground? or does that rad alt call “ fifty”when the gear is 50ft above the ground?. I don’t think it calls it when the gear is at 50ft because it so often appears to call it exactly when we cross the threshold.
50ft call is at 50ft Rad Alt. Based on the antenna position and body angle the gear will often be lower, as you can see from the picture in the previous post. In my airplane around 25ft lower.

hans brinker 15th Dec 2018 02:43
Originally Posted by ManaAdaSystem (Post 10335881)


Thanks, but I go below the GS when it is needed. On nornal landings I just follow the GS or PAPI.
Sorry, but it should never be needed. Either you have enough LDA to land in the touchdown zone, or you go somewhere else. Just because you haven't hit the runway lights doesn't make it ok.

Reluctant Bus Driver 15th Dec 2018 03:07
Anyone have access to 737-700 landing data? It would be interesting to see what the margins where. Even if legal it had to be pretty tight..

Reluctant Bus Driver 15th Dec 2018 03:17
As some have alluded to, the usable landing distance, assuming they did not go below GS, is 4575ft. Not much to hang your hat on..

ManaAdaSystem 15th Dec 2018 14:17
Originally Posted by hans brinker (Post 10336030)
Sorry, but it should never be needed. Either you have enough LDA to land in the touchdown zone, or you go somewhere else. Just because you haven't hit the runway lights doesn't make it ok.
On paper I agree with you 100%. In real life I am very aware that braking action during winter operations is not an exact science. So, I add 100 - 200 m to the 12 m margin my calculations give me. I can pretty much guarantee that if you spent a few days in my cockpit to see what we do in the winter season on short, contaminated runways situated near high terrain, with moderate turbulence, snow showers, wind and 4 degree glide slopes... you would do the same.

ManaAdaSystem 15th Dec 2018 14:57
Originally Posted by Reluctant Bus Driver (Post 10336036)
Anyone have access to 737-700 landing data? It would be interesting to see what the margins where. Even if legal it had to be pretty tight..
On a 5800 ft (1768 m) wet runway with 10 kts tailwind, 56 tons, my tool says he would need max autobrakes.
FL30 1409 m actual landing distance.
FL40 1380 m actual landing distance.

Sailvi767 15th Dec 2018 15:18
Originally Posted by ManaAdaSystem (Post 10336350)


On a 5800 ft (1768 m) wet runway with 10 kts tailwind, 56 tons, my tool says he would need max autobrakes.
FL30 1409 m actual landing distance.
FL40 1380 m actual landing distance.



Were those numbers using fair braking action to account for the heavy rain?

ManaAdaSystem 15th Dec 2018 20:55
Originally Posted by Sailvi767 (Post 10336358)


Were those numbers using fair braking action to account for the heavy rain?
There are no options for «heavy rain» in my performance tool, and my calculations are based on our aircraft options. Which may or may not be the same as the SWA aircraft. I believe BA Good is used for a wet runway, however I have never had any braking problems on a wet and grooved runway.
India + Wet + Monsoon + Rain = a different story.

172_driver 15th Dec 2018 20:57
50ft call is at 50ft Rad Alt. Based on the antenna position and body angle the gear will often be lower, as you can see from the picture in the previous post. In my airplane around 25ft lower.
If the 50-call occurs at the exact moment the antenna is 50 ft off the ground, the lowest point of the landing gear would be at 25 feet. Yet touch down occurs as the radio altimeter reads 0. Something doesn't add up in my head......

Reluctant Bus Driver 16th Dec 2018 02:52
Originally Posted by ManaAdaSystem (Post 10336350)


On a 5800 ft (1768 m) wet runway with 10 kts tailwind, 56 tons, my tool says he would need max autobrakes.
FL30 1409 m actual landing distance.
FL40 1380 m actual landing distance.



Usable glide slope landing length, assuming they did not go below, is 4575ft. Flap 40 actual landing distance is 1380m=4527ft. A legal margin of 48 ft? I am not trying to split hairs here, I am simply saying that looking at total runway length and equating it to legal landing distance is not correct. You have to look at available runway distance. It's an easy mistake. I know because I have made the same mistake, just not with consequences! On a razor thin margin like what happened in BUR it could be the difference between taxiing to the gate or ending up in the EMAS..


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