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Faro
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Displaced Thresholds With An Approach Over Water?

Tue Jul 28, 2009 8:21 pm

In the following pic off the database, why the displaced threshold if your approach is over a water surface? Where is your obstacle; don't understand...


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Faro
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KELPkid
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RE: Displaced Thresholds With An Approach Over Water?

Tue Jul 28, 2009 8:47 pm

Maybe on the other end of the lake  Wink (after all, this is in Dallas, Texas, a very land-locked city!)
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Faro
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RE: Displaced Thresholds With An Approach Over Water?

Tue Jul 28, 2009 8:54 pm



Quoting KELPkid (Reply 1):
Maybe on the other end of the lake   (after all, this is in Dallas, Texas, a very land-locked city!

My bad...when I saw NAS I automatically assumed it were out on the Gulf coast. Dallas-on-Lake, how exotic...

Faro
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2H4
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RE: Displaced Thresholds With An Approach Over Water?

Tue Jul 28, 2009 9:25 pm



Quoting Faro (Thread starter):
why the displaced threshold if your approach is over a water surface? Where is your obstacle; don't understand...

I wonder if shipping lanes (at other airports) might justify displaced thresholds for clearance above passing ships.

2H4
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vikkyvik
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RE: Displaced Thresholds With An Approach Over Water?

Tue Jul 28, 2009 9:59 pm



Quoting 2H4 (Reply 3):
I wonder if shipping lanes (at other airports) might justify displaced thresholds for clearance above passing ships.

 checkmark 

Look at the info for runway 4R-22L and 22R at BOS:

http://www.airnav.com/airport/KBOS

For 4R:

Obstructions: 157 ft. boat, lighted, 1550 ft. from runway, 8:1 slope to clear
APCH RATIO 17:1 FROM DSPLCD THR; 43:1 WHEN CHANNEL IS CLEAR.


for 22L:

Obstructions: 45 ft. boat, 525 ft. from runway, 7:1 slope to clear
APCH RATIO 38:1 FROM DSPLCD THR.


for 22R:

Obstructions: 44 ft. boat, 670 ft. from runway, 10:1 slope to clear
APCH RATIO 33:1 FROM DSPLCD THR; 50:1 TO THR WHEN CHANNEL IS CLEAR.
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MSNDC9
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RE: Displaced Thresholds With An Approach Over Water?

Wed Jul 29, 2009 5:41 pm

Quoting Faro (Thread starter):
In the following pic off the database, why the displaced threshold if your approach is over a water surface? Where is your obstacle; don't understand...

You still have a runway safety area requirement "before" the threshold which is 600-feet. Water cannot serve as an RSA beyond the runway, so in terms of lighting layouts, distance remaining markings and needs of an RSA of 1,000-feet in that area (going the other direction), they probably made it 1,000-feet to make it even then applied declared distances. It also has the unusual 3,000-foot ALS vs the standard 2,400-foot.

They did a similar thing at the other end. The threshold is even with a 1,000-foot RSA to the property line.

[Edited 2009-07-29 10:48:08]
 
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RE: Displaced Thresholds With An Approach Over Water?

Wed Jul 29, 2009 8:31 pm

[quote=Vikkyvik,reply=4]

Quoting 2H4 (Reply 3):
I wonder if shipping lanes (at other airports) might justify displaced thresholds for clearance above passing ships.



Look at the info for runway 4R-22L and 22R at BOS:

http://www.airnav.com/airport/KBOS


I have been out doing engine runs at the end of a closed runway here in BOS and heard the controllers tell the inbound airplanes to go around due to a Oil Tanker in the channel on the approach end of 22L and 22R.

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EcuadorianMD11
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RE: Displaced Thresholds With An Approach Over Water?

Thu Jul 30, 2009 12:51 am

I remember towing an oil rig (jack up) through Singapore Straits and the vessel traffic controller was pretty anxious for us to report our position at a particular point to tell Changi Airport in time.

If you catch a jetliner with the legs of an oilrig..........I guess you´d make the headlines!
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Woodreau
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RE: Displaced Thresholds With An Approach Over Water?

Fri Jul 31, 2009 5:28 pm

Quoting MSNDC9 (Reply 5):
You still have a runway safety area requirement "before" the threshold which is 600-feet. Water cannot serve as an RSA beyond the runway, so in terms of lighting layouts, distance remaining markings and needs of an RSA of 1,000-feet in that area (going the other direction), they probably made it 1,000-feet to make it even then applied declared distances. It also has the unusual 3,000-foot ALS vs the standard 2,400-foot.

They did a similar thing at the other end. The threshold is even with a 1,000-foot RSA to the property line.

I was thinking along the same lines as you were with respect to the runways safety area and approach lighting.

At first I thought there might be high voltage transmission lines just south of the runway - there aren't any. However, what the photo doesn't show is that there is a radio/television tower antenna farm perched on a hill about 6-7 miles south along the extended centerline with several antennae - I think around 4 or 5 - that go up to 2500ft above the touchdown zone elevation. Given that a 3 degree ILS glideslope is 300ft / nm - it might affect the threshold, but I don't think that in itself determines the displaced threshold - the antennae would just interfere with any instrument approaches from the south.

This particular runway is closed but the city has elected to continue maintaining the runway in the event it is needed again. I believe Vought Aircraft still does use it to fly parts in and out of the production facility.

[Edited 2009-07-31 10:29:51]
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KELPkid
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RE: Displaced Thresholds With An Approach Over Water?

Fri Jul 31, 2009 6:00 pm



Quoting Woodreau (Reply 8):

At first I thought there might be high voltage transmission lines just south of the runway - there aren't any. However, what the photo doesn't show is that there is a radio/television tower antenna farm perched on a hill about 6-7 miles south along the extended centerline with several antennae - I think around 4 or 5 - that go up to 2500ft above the touchdown zone elevation. Given that a 3 degree ILS glideslope is 300ft / nm - it might affect the threshold, but I don't think that in itself determines the displaced threshold - the antennae would just interfere with any instrument approaches from the south.

IIRC, in the 1980's, an F-14 had an unfortunate encounter with one of the towers (a TV station maintained by late former boss and flight instructor)...maybe this is what lead to the displaced threshhold. I don't remember the details, but I think the flight crew was killed, and a TV station had to operate with an emergency authorization from the FCC (which allowed them to temporarily relocate their transmitter to an adjacent tower at a lower height) until their tower could be reconstructed...
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