GO AROUNDS FROM ILS

[DESCEND WHEN READY]

I fly IFR light twin charter. I use the ILS minima eg 250 feet plus 50 feet for Pressure error correction. Do those in the jets go down to the stated minima eg 250 feet and if a go around is necessary do you lose alot of height before the TOGA power arrests the descent rate. If a go around is possible do you have a higher power setting to arrest the sink earlier?

[Zeke]

Radar altitude is also used

[OzExpat]

I design instrument approach procedures and can assure you that a certain amount is allowed for "sink thru" in calculating the DA/DH. The concept of being prepared to go around at DA/DH is based on the assumptions made in the design of the procedure. It will vary for different categories, but isn't a good idea for you to bust the DA/DH in the hope of seeing something!

Yeah, yeah... I know... :eek:

As for the altitude actually used by different aircraft types, it all depends on what, if any PEC is required. For example, I know that in my B200, PEC is zero, so I don't need to make any adjustments. Likewise for any aircraft types where PEC might be a negative value.

[Eff Oh]

Yes, a factor is built in for sink through. I thought it was 50ft. Not too sure! :confused:

Anyway on a side note. It is not uncommon on a "low viz" approach, (using a Radio Decision Height RDH) to actually touchdown during a Go-Around from low level. This is due to the "sink through" and is perfectly safe!! Have to say it has never happened to me yet. However I once flew a go-around from 14ft radio alt and didn't touch down!! in the sim of course!! :D :D :D

Eff Oh

[ 03 December 2001: Message edited by: Eff Oh ]

[sudden Winds]

If your decision of going around or landing is made at the DA, you WILL go below DA. If you check the practical test standards for the instrument rating in the US it says you can maintain your MDA plus +50/-0 ZERO. That´s ´cause you´re leveling off at that altitude.
When mentioning DA margins it specifies a -50 feet margin. This is ´cause they know you´ll go slightly underneath it, even in a 172.
For example. Let´s say a 747 approaching at 150 knots groundspeed, flying a 3º glideslpe the rate of descent will be close to 750 feet per minute, maybe a bit more (I do Groundspeed times 5) If that plane reaches DA
(H)and doesn´t see anything, it must go missed. The maneuver is preety sudden, I´ve done it, but there´s no way the aircraft will initiate an immediate climb without losing 50 feet or so. TERPS knows this and ILSs are flight checked with that taken into account.

Glideslopes are flight inspected all the way to 100´(CAT 1), I´ll get back to that.

I would like to say that unless you´re flying a CAT II or III approach, heights in parenthesis ARE NOT radio altimeter heights. They are the difference between the altitude at that position and the Touchdown zone elevation of that runway.
Unless you are flying a CAT II or III you´re required to use your altimeter to determine when it´s time for you to decide whether to continue approaching or go around.

In the States, the required RVR for an ILS CAT I is 2400 ft (1800 ft if the airport has touchdown zone lights)
When the airplane is at the DH, it is usually at some 4,000 feet distance from what´s called the ground point of intercept, where the glidepath meets the ground, and it is at 3,000 feet from the landing THRESHOLD, roughly.
If that day RVR is 2400 feet the airplane will not see the runway at the DH, if he doesn´t see the runway, obiously he won´t see the the PAPI or VASI, located at another 1000 feet down the rwy.
However, if he sees the Approach light system, he is allowed to continue descending to 100 feet above the touchdown zone elevation.
The portion of flight from the DH to 100 feet above tdze is what´s called COMPOSITE FLIGHT, a combination of instrument and visual.
The pilot can use visual references to determine runway alignment, and bank information, but he still uses the glideslope and the ADI to monitor his profile and pitch. At 100 feet above tdz the aircraft will be at 1,000 feet or so from the landing threshold, and at another 1,000 feet from the touchdown point. He still needs an extra 400 feet to see the far VASI light so there you have 1000+1000+400 equals 2400, so that´s why ILSs require RVR 2400 feet. At that time, the pilot sees the lights, the runway, and the VASI. He can now continue 100 percent visual...Plus at 100 feet above tdz you are supposed to stop using the electronic glideslopes, since they´re not flight inspected below 100 feet.
Hope it helps.

Good luck to you all !!!

[jtr]

Doing a LWMO ILS with a DH of 22 feet, initiate the go-around at DH, you will touchdown in both the 340 (firmly)and the 330 (just).

[DESCEND WHEN READY]

THANKS FOR THE COMMENTS GUYS. ITERESTING JOB YOU HAVE EXPAT!

[OzExpat]

DWR... my job has it's moments...

[CaptainSquelch]

To get back to your original posting DWR; we don't use a higher power setting to arrest a sink rate before a G/A is started. In fact the power is only secondary in a G/A with a big jet. On the sim we used to do this demo for peolpe conveting from props: Go around without changing the pitch and just add power. You'd hit the ground around the touchdownpoint with a speed well above you threshold speed. Then Goaround without power and just pitch up. You'd hear the stall warning depending on the weight a some two to three hundred feet above DA/DH. This was to demonstrate the importance of pitch in a G/A

Sq

[Chimbu chuckles]

DD I fairly certain that was not the point of the demo. :D

Chuck.

PS. Ozexpat, try to tell the clever dicks at PX that you're allowed to dip under DA in the GA and they would give you a severe talking at! Too long in the jungle I suppose!

[OzExpat]

Chuck... I haven't had anyone at PX dispute me on it over the years, but I wouldn't be surprised to encounter it. This is the dreaded MDA mindset at work, I fear. From my own observations, this mindset isn't restricted to Pixie.

I've overheard similar things at various Aero Club bars and even in hotel lobby bars, where the people discussing it are professional aircrew for various high-profile international airlines.

I just hope that some of them have been lurking around this thread.

[A Very Civil Pilot]

Don't Carrier Aircraft land with full power, just in case they miss the hook and end up doing a touch & go instead?

[CaptainSquelch]

Thanks Chuck, that was indeed not the intend of the demo. I may have not explained myself clearly.
Douglas, the demo was performed from a normal, stabilized ILS (or any other stabilized approach with a glide of around 3 degrees). In the "G/A without power" I should have said that there was no power added above the normal power on the approach.

The impact on the trainees was normally rather profound and next time they'd certainly have their pitch correct :D