Too High on the Glideslope

RNAV, GNSS, GPSS. Your place to discuss all aspects pertaining to Instrument Flying.

Moderator: Moderators

User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Sat Oct 22, 2016 9:21 pm

Hi quintdxb,
SR22 G3
2xGarmin 430 Nav com's
Stec55 autopilot
Hop
There is no gravity...the Earth sucks
jalopysled
Taxiing
Posts: 72
Joined: Thu Sep 13, 2007 1:00 pm
Closest Airfield: FACT
Has liked: 0
Been liked: 0

Re: Too High on the Glideslope

Unread post by jalopysled » Sun Oct 23, 2016 8:32 am

Another good one Hop - you sure are FINDING interesting topics for discussion!

My 2c... it is a bit taboo to intercept from above, mostly for fear of problematic GS indications (the Kiwi B767 comes to mind).

Although it CAN be done if you set limits for yourself and carry it out in a controlled manner.

Problem 1 - False GS or erroneous GS indication.
This will be solved by keeping the glide path angle in mind every couple miles (3 x dist). But this you'll be doing in any case, right?

Problem 2 - Some autopilots will not capture a GS when not LOC established, so you'll need to mode change a bit - plenty of threats here, especially if single crew! (Think - select VS, high ROD... is APP still armed? Plenty of scanning, a freq change or 2, ATC etc - ooooooo s#%¥ way below GS now!)
Solve this by picking a hard floor - say to 1000ft AGL and no lower, else you give the approach away.

Problem 3 - chasing the ever-elusive sweet spot - say your approach speed is 100kts, require ~500pfm ROD. you're now above GSlope, increase your ROD to 600fpm - but that will increase your Ground Speed - so now you're at 120kts... still not going to capture, so you nose-over more, increase your ROD, your GS increases and with it your required ROD increases.
Solution - sloooooow down - keep your approach speed while increasing ROD to regain the GSlope.

Earlier someone mentioned setting up an "Early Warning" for LOC movement by using the VOR - it was mentioned setting up the inbound radial, and when the inbound radial is 1/2 scale then the LOC will start to liven up. The number is actually when the inbound radial is ONE DOT, the LOC will start to move off full scale. LOC is 4 x more sensitive than the VOR.
User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Tue Oct 25, 2016 8:19 pm

Hi Jalopy,

I think a HSI/GS indicator does this at half scale while a stand-alone VOR indicator does this at one dot??
Hop
jalopysled wrote:
Earlier someone mentioned setting up an "Early Warning" for LOC movement by using the VOR - it was mentioned setting up the inbound radial, and when the inbound radial is 1/2 scale then the LOC will start to liven up. The number is actually when the inbound radial is ONE DOT, the LOC will start to move off full scale. LOC is 4 x more sensitive than the VOR.
There is no gravity...the Earth sucks
jalopysled
Taxiing
Posts: 72
Joined: Thu Sep 13, 2007 1:00 pm
Closest Airfield: FACT
Has liked: 0
Been liked: 0

Re: Too High on the Glideslope

Unread post by jalopysled » Fri Oct 28, 2016 9:35 pm

Hop Harrigan wrote:Hi Jalopy,

I think a HSI/GS indicator does this at half scale while a stand-alone VOR indicator does this at one dot??
Hop
jalopysled wrote:
Earlier someone mentioned setting up an "Early Warning" for LOC movement by using the VOR - it was mentioned setting up the inbound radial, and when the inbound radial is 1/2 scale then the LOC will start to liven up. The number is actually when the inbound radial is ONE DOT, the LOC will start to move off full scale. LOC is 4 x more sensitive than the VOR.
It does depend on the HSI yes - but more so if it's a digital HSI, because then it switches sensitivity. But if you have it tuned to a VOR for early warning of LOC movement - then VOR sensitivity would apply. (Not too great an idea to have Nav 1 tuned to a VOR when you're turning inbound for the LOC - been there, got the brown underpants... After that I just used Nav 2 with inbound radial, nav 1 with LOC)
Whereas if it is a steam-driven HSI (receives signals purely from radio nav), then it would depend on how many dots it has.

VOR full scale deflection - 10*, so 1 dot on a 5-dot indicator is 2*
ILS full scale deflection is 2.5*, so just over 1 dot when tuned to VOR will the LOC only start moving off full scale.
Plettflyer
Fuelling up
Posts: 34
Joined: Fri Nov 11, 2016 3:45 pm
Closest Airfield: FAPG
Has liked: 2 times
Been liked: 0

Re: Too High on the Glideslope

Unread post by Plettflyer » Fri Nov 11, 2016 10:20 pm

Setting up a VOR radial to warn of impending localizer movement is a good idea. Just make sure of the geographical location of the VOR transmitter in relation to the runway. In most cases they are located close to the runway, but not always.
User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Sat Nov 12, 2016 8:46 am

Hi Plet flyer,
Only issue doing that is that you then have to remember to switch the Nav radio over to the localiser at a busy time in the approach, unless you have two VOR displays (which my PFD does not)
Hop
There is no gravity...the Earth sucks
MemyselfandI
Engine full power confirmed
Posts: 186
Joined: Sun Dec 04, 2011 9:03 am
Has liked: 0
Been liked: 6 times

Re: Too High on the Glideslope

Unread post by MemyselfandI » Thu Dec 08, 2016 7:25 am

Chaps, as someone already posted the ICAO doc which specifies a straight and level portion, you are the PIC and as such have the right to reject the vector if you feel it's too close thereby making you too high. ATC's do sometimes err as I suspect the GG one may have done. My point is, if you're not happy with a clearance...SAY SO ! For some reason you pilots seem hesitant to call out when things aren't quite kosher...why??? Look at this latest fuel issue in Colombia, the crew didn't say a word until it was too late!
We are there FOR you...USE us !!
Slick
Taxiing
Posts: 76
Joined: Wed Aug 21, 2013 1:11 pm
Closest Airfield: FAOR
Location: Johannesburg
Has liked: 7 times
Been liked: 3 times

Re: Too High on the Glideslope

Unread post by Slick » Sat Dec 17, 2016 10:26 am

Hi Hop

I see what you are saying with regards to switching over from the VOR to the ILS during a busy period, however on the Garmin you are using, you should be able to program the ILS in for standby purposes (Proc button). Especially when flying a system with more than one screen, pressing Proc, Activate Vector to final should switch both screens over to the ILS frequency and final approach course, and this saves you both time and workload. This also helps you keep your HSI needle alive for situational awareness until you are ready to switch across.

Just my 2c on the Garmin system, hope it helps!

Derek
User avatar
ACE MAN
Tree Tousand
Tree Tousand
Posts: 3930
Joined: Tue Apr 10, 2007 7:53 am
Closest Airfield: FAKT+VHHH+FAPX
Location: iKhaya mina 22N114E
Has liked: 330 times
Been liked: 75 times

Re: Too High on the Glideslope

Unread post by ACE MAN » Sat Dec 17, 2016 4:07 pm

Keeping your track miles in mind x3 (3.2 actually) at initial approach speeds will place you in a good position as to where you should be on a CDA , if you have not got this sorted out but higher by the time you are 8nm from touchdown you will be high on the GS. If the intercept is then done from above but not achieved by the FAF and stable rather throw the approach away and go-around!
Simple for pilots as you only need to know the 3 x table 8) ie 6000'AAL at 20nm, 4500'AAL at 15nm, 3000'AAL at 10nm,1500'AAL at 5nm, 900'AAL at 3nm, 300'AAL at 1nm etc. This keeps the noise down and saves you fuel. Obviously you need to keep the above in respect to terrain and within the MVA. Any ATC worth his salt would ask you if you are OK for height if he can see you are edging on the High side. Keep your mental math going to know where you are in a point in space at all times!
IITYWTMWYBMAD
Nomakhanjani
¯¯VAF¯¯
User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Sun Dec 18, 2016 10:08 pm

Hi Slick & Aceman,
Great advice, thank you.
btw...do you recommend keeping a GPS display running during the ILS approach, or is this just a distraction and better to concentrate on the ILS display only?
Hop
There is no gravity...the Earth sucks
Slick
Taxiing
Posts: 76
Joined: Wed Aug 21, 2013 1:11 pm
Closest Airfield: FAOR
Location: Johannesburg
Has liked: 7 times
Been liked: 3 times

Re: Too High on the Glideslope

Unread post by Slick » Mon Dec 19, 2016 7:49 am

Hi Hop

Only a pleasure, I hope it actually helps.

I always have the MFD displaying the final approach track after selecting Vector to Final, which definitely helps again with situational awareness, but I don't pull too much information from the MFD except for the engine parameters while flying the ILS. I have found that the Flight Director on the Garmin is remarkably accurate so there's not much need to turn away from the PFD.

I do understand though that the G950 might be slightly different to your version though. :)

Derek
User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Mon Dec 19, 2016 8:17 am

Ace man...next question pls...if you're on a 45deg intercept to the localiser, how does your 300'/nm calculation fare prior to intercepting? You will be approaching the ext centerline at an angle, is the check still valid?
Hop
There is no gravity...the Earth sucks
User avatar
ACE MAN
Tree Tousand
Tree Tousand
Posts: 3930
Joined: Tue Apr 10, 2007 7:53 am
Closest Airfield: FAKT+VHHH+FAPX
Location: iKhaya mina 22N114E
Has liked: 330 times
Been liked: 75 times

Re: Too High on the Glideslope

Unread post by ACE MAN » Mon Dec 19, 2016 8:51 am

I agree with slick, good to have some kind of Nav display, much better awareness than the old clocks and dial days. On your 45deg or base to intercept question, if you are doing the 3x table on the DME you will of course be slightly low, work out your track mile and it is more accurate, that information could come from a distance to go to threshold on the GPS. Be very careful if you are doing any of these calculations in a procedural environment, respect the plate and MSA , i.e. TERRAIN and obstacles. Hope this is helpful to your questions.
IITYWTMWYBMAD
Nomakhanjani
¯¯VAF¯¯
User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Mon Dec 19, 2016 4:06 pm

Hi Aceman,
Many thanks for the advice!
I will appreciate it if you could offer your opinion on the subject in my next posting (coming up shortly)!'Hop
There is no gravity...the Earth sucks
User avatar
Hop Harrigan
1k poster
1k poster
Posts: 1012
Joined: Tue Jun 01, 2010 7:55 pm
Has liked: 3 times
Been liked: 19 times

Re: Too High on the Glideslope

Unread post by Hop Harrigan » Tue Jan 03, 2017 6:41 pm

Hi Plettflyer,
Nice meeting you today at the hangars!
Cheer,
Hop
There is no gravity...the Earth sucks

Return to “Instrument Flying”