Scudrunners

[quote author=red_shiny_ribbon link=topic=5407.msg13982#msg13982 date=1484701226]
[quote author=ScudRunner link=topic=5407.msg13961#msg13961 date=1484611318]
Gees a DH of 100 feet in a 747 your mains are probably on the ground already.
[/quote]


This right here is proof enough that you bush pilots like to talk and judge way out of your league. No the mains would not be on the ground by DH, the redar altimeter is calibrated for wheel height.
[/quote]


Yes, and you come off sounding like the paragon of aviation knowledge.

Best I can determine, with the tail scraping the ground the pilots eyes are at about 50’.

747-400 eye to ground height is about 28.5’.

Cockpit to main gear is about 100’.

Trig says that the line from cockpit to main gear is 104’ at a 15.9 degree angle. Add 12 degrees to that (Boeing’s tail strike pitch spec) and reverse the math and you get a height of just under 50 feet. Let’s knock a bit off because hopefully no one’s making an approach at such an insane pitch angle, so say 40’.

I'm just a deplorable - I'm not one of Hairdo Dolly's Air Canada
pretty boys that like to drill holes in the runway at Jamaica - but
I will wager an Andrew Jackson with anyone that contends a 747
that initiates a miss at minimums during a cat II approach (at
100' DH) [i]isn't[/i] going to touch down on the runway during the
overshoot.

The radar alt in most transport category aircraft is calibrated to read 0' at main gear touchdown. The RA actually reads in a negative value when the main gear is on the runway to allow for auto lands (We can use 0 ceiling and 50 meters RVR where I work.) I do fly the -400 (12 years on the old girl and now the 777 and soon the '78) The basics are the same...radar alt is going to read 0 at main gear touchdown. The CAT III B or A or CAT II are an auto land where I work and it can be done with one engine shut down with no real penalty. If the weather is below CAT I, again, auto land, but that's a company minima. The time to consider a change in destination or diversion is when the options start to disappear. No reason to divert if yo[font=verdana]ur weather is at limits, unless it's because your fuel limits have been reached or your Ops manual requires various runway/weather options to be fulfilled. Incidentally the ILS Glide Slope receiver actually is in two places on the B744, it is automatically switched to the nose gear doors at a certain height in order to facilitate a correct height readout and clear reception point due to body angle at touch down. The airport in question was built by the Yanks to standard to facilitate easy access to Afghanistan for the USAF etc, and is a ICAO standard airport which means it meets the requirements for most carriers to use as a destination and alternate airport. The decision to land during the weather perorated is normal operations to a majority of carriers. The cause has yet to be determined so I won't bother to guess. Sad day though.[/font]


Be safe everybody!


PS: Mr Jansen has done a nice job explaining the various requirements for low vis ILS' and I hope I didn't duplicate
any of his work...

Just had a quick look in the books to confirm (for A340). 747-400 is probably not that different.

Radio altimeters are mounted on the aft fuselage behind the main wheels.

Localiser and Glideslope antennas are mounted in the nose with a second Glideslope antenna down by the nosegear.

For the A340-500 crossing the threshold at 50' on an ILS approach:-

Pilot is at 65' Main gear is at 34' (31' eye to wheel height).

@Colonel Sanders

You'd lose that bet!  :)

Engines are normally operating at a fairly high thrust level on approach - acceleration to full thrust is probably about 2 seconds.

Speed on approach is 1.3Vs so the wing still has a lot of lift (energy) available. As soon as you increase the pitch attitude (angle of attack) the extra lift will rapidly arrest any descent. The thrust will kick in before you lose airspeed.

For altitude loss on a go-around figures I have are 10' with stabilised thrust and 35' with idle thrust (A340-500 with a max landing weight of 541,000lbs). Real world figures are probably not quite as good but a momentary touchdown shouldn't happen until you start a go-around from below 50'.

Rate of descent 800fpm - takes just over 7 seconds to ground contact from 100' and just over 3.5 seconds from 50'

For an example of how much energy is available in a wing on landing look at the EK521 crash - they managed to get the aircraft to 85' on a go-around after a landing with thrust at idle.

[quote author=red_shiny_ribbon link=topic=5407.msg13982#msg13982 date=1484701226]
[quote author=ScudRunner link=topic=5407.msg13961#msg13961 date=1484611318]
Gees a DH of 100 feet in a 747 your mains are probably on the ground already.
[/quote]


This right here is proof enough that you bush pilots like to talk and judge way out of your league. No the mains would not be on the ground by DH, the redar altimeter is calibrated for wheel height.
[/quote]

Thanks for the complement, I use to love landing on sandbars and the sides of mountains but i'm kind of slow ive been told. Now I take it easy and land on straight pavement ILS to ILS like any muppet can do.

I wonder if red-shiny uses PMA during his/er approach and landing?

[quote author=Chuck Ellsworth link=topic=5407.msg13985#msg13985 date=1484704182]
When you are stabilized on the approach in the approach attitude in a 747 you maintain a slight nose up attitude?


How do you determine what a slight nose up attitude should be?
[/quote]


You don't determine what your nose-up attitude should be, you fly at the proper speed and the attitude is what it is. Pretty much like most aircraft. The pitch attitude will vary depending on flaps setting and actual approach speed. That being said, one would expect for many big jets to be about 2-3 degrees nose-up.

Here's a very interesting plot of the ADS-B data.

[url=http://www.pprune.org/rumours-news/5896 ... ost9646277]http://www.pprune.org/rumours-news/5896 ... ost9646277[/url]

Not clear if the data is accurate.

It shows the aircraft above the profile - leveling off - then making a 3 degree descent into the ground.

Seems (if the ADS data can be relied on) that they MIGHT have been trying to catch the GS from above and in a heavy jet it's not ideal. It can be done with the proper coordination but if the standard for stabilized approaches can't be met, a Go Around is the right call...

Looks like the ADS-B data is correct. The overflew the runway well above the ILS profile and touched down 900m beyond the end of the runway.

Looks like they just flew it into the ground without realising where they were.