Displaced ILS question

[clicker]

Hope you don't mind me asking this question here but some of you know my "name" as a regular on Capcon.

I was taking a look at the AIP entry for Lydd and noticed that the ILS loc was off to the side of the rwy rather than on the centreline and that it was had a 5 deg offset. I presume it's put to the side so that the offset loc beam is directly over the runway touchdown point?

My question is when you clever lads and lasses fly an ILS like this do you kick off the offset in the same way you would do with the drift from a crosswind approach or is there a different way of touching down off that ILS.

I did also see that the remarks state no auto coupled approaches allowed below 250ft but that makes sense, after all you don't want to end up in a field beside the ILS loc aerial.

[A and C]

Just fly it in the normal way and as soon as you get enough visual reference position the aircraft in the same way as you would on a normal visual approach.

The DA of 430 FT ( 418 DH ) is a long way above the ILS system minima, I am guessing that along with the modest runway approach lighting the FAT ofset is the reason for the DH being 218 ft above the ILS system minima to enable time for the visual maneuver.

[clicker]

Thanks.

Didn't think of checking the minimums etc.

Just as well I failed the eyesight test in the PPL medical then :E

[RequestPidgeons]

Hey, Clicker

You are keeping us all honest.

Thank you!

:ok:

[Davita]

The worst offset ILS I encountered in my career was the old Hong Kong airport at Kai Tak...... r'way 13
Here is an interesting wikipedia of that approach using offset ILS.

"The landing approach using runway 13 at Kai Tak was spectacular and world-famous. To land on runway 13, an aircraft first took a descent heading northeast. The aircraft would pass over the crowded harbour, and then the very densely populated areas of Western Kowloon. This leg of the approach was guided by an IGS (Instrument Guidance System, a modified ILS) after 1974.
Upon reaching a small hill marked with a huge "aviation orange" and white checkerboard used as a visual reference point on the final approach (in addition to the middle marker on the Instrument Guidance System), the pilot needed to make a 47° visual right turn to line up with the runway and complete the final leg. The aircraft would be just two nautical miles (http://en.wikipedia.org/wiki/Nautical_mile) (3.7 km) from touchdown, at a height of less than 1,000 feet (300 m) when the turn was made. Typically the plane would enter the final right turn at a height of about 650 feet (200 m) and exit it at a height of 140 feet (43 m) to line up with the runway. This manoeuver has become widely known in the piloting community as the "Hong Kong Turn" or "Checkerboard Turn". Amongst passengers it became known as the "Kai Tak Heart Attack (http://en.wikipedia.org/wiki/Heart_Attack)".[18] (http://en.wikipedia.org/wiki/Kai_Tak_Airport#cite_note-18)
Landing the runway 13 approach was already difficult with normal crosswinds since even if the wind direction was constant, it was changing relative to the aircraft during the 47° visual right turn. The landing would become even more challenging when crosswinds from the northeast were strong and gusty during typhoons. The mountain range northeast of the airport also makes wind vary greatly in both speed and direction. From a spectator's point of view, watching large Boeing 747s banking at low altitudes and taking big crab angles during their final approaches was quite thrilling. Despite the difficulty, the runway 13 approach was nonetheless used most of the time due to the prevailing wind direction in Hong Kong.
Due to the turn in final approach, ILS (http://en.wikipedia.org/wiki/Instrument_Landing_System) was not available for runway 13 and landings had to follow a visual approach. This made the runway unusable in low visibility conditions."

We used to do this on B707 in typhoon conditions but stopped when big fanjets were used as the fan could not handle the shifting winds.

[clicker]

I've seen a video of that HKK approach. Scary or what. Left at the flats, right at the boards. That said as I like flying I would loved to have been in a jump seat for that.

While I failed that medical I did work for an airline for 7 years (ops at LGW) so managed a few jump seat trips, always interesting. Gets too boring in the back, I prefer to know where I am.

[Basil]

I prefer to know where I am.
Wish I had, every time I flew :}

[Davita]

Not trying to be a smartass clicker but Hong Kong designator is HKG...HKK is Hokitika in New Zealand.

I'm saying this because my wife's galpal visited us in Bali recently. Trouble is... she booked her flight to Balikpapan!
There was confusion between my wife and her pal on facetime until I said "just cancel your BPN destination and book to DPS." Which is Denpasar, Bali's airport.
Sometimes airport designators, on the internet, are easier to identify than airport names.

I also recall some honeymoon couple booked what they thought was a flight from UK to Sydney, Australia but wrote Sidney, which is in BC, Canada. They wondered why there was a stopover in Nova Scotia.:confused:
The good news....when everyone in Canada learned of their misfortune, they became celebrities and had the best honeymoon and memory of it.

I suggest you stick to the small aircraft as per your hobby...the big ships in the sky are boring and automated. In a few years I predict they will be flown like drones....they already test driverless cars.
A friend of mine has one that parks itself....we're nearly there!

[OvertHawk]

Don't have a plate in front of me at the the moment, but is the reason for the offset LOC at Lydd not due to the presence of the prohibited area for the Nuclear power station nearby? If it was a direct LOC i think it would take you through the prohibited area.

Standing by to be corrected...

OH

[Exascot]

I always thought that we would land with laundry on the starboard wing tip one day off the lights on top of the flats.

[Davita]

It looked worse than it probably was but not in a x-wind when the turn could so easily be overcooked. I lived in the 18 floor of the apartment block with a view of the checker board and have witnessed many who turned too soon and couldn't get back to the 130deg centre line and gone around.
The CX guys, more familiar with the approach than others, let the A/C go closer to the checker board and, given the wind prevailed from N.E., let it help in the turn and cut down the angle to line-up.
The offset IGS was only used to avoid obstructions and get down to minimum...the rest was the old grunt style of flying by the pants.

[CoffmanStarter]

Clicker ...

IIRC the 5 ̊offset is to keep the RWY 21 ILS approach clear of the D141 (Army Ranges)

See Plate Notes re intercept at 900m before THR

http://i1004.photobucket.com/albums/af162/CoffmanStarter/image_zpsfd924913.jpg

Credit : NATS Doc - Not For Navigation

Missed approach requires a Right Turn to avoid the Power Station and Army Ranges shown.

More here ...

NATS Lydd EGMD (http://www.nats-uk.ead-it.com/public/index.php%3Foption=com_content&task=blogcategory&id=98&Itemid=147.html)

[Basil]

Davita, Reminds me of a new FO in a well known UK airline whose bidline seniority was not conducive to going anywhere desirable. He was, therefore, surprised and delighted when he was awarded the tripline for which he'd bid containing two LOS flights.

Clue: It ain't LA :E

[chevvron]

Sumburgh has offset LLZs on both runways; Odiham has one too on runway 27.
They're not uncommon but can never be Cat 1 and the minimum DH is 250ft as opposed to 200ft with an inline Cat 1 LLZ.

[clicker]

Davita

That will teach me to rely on my memory without checking!

Coff,

Thanks I had discounted the power station from the ILS side having visited the area's RSPB reserve there trying to photograph a Bittern there. Heard it booming but never saw it.

Had also forgotten about the Lydd ranges although had used the area to help train some air cadets for a couple of Nijmegen marches back in the 70's.

[EngAl]

Gaydon had an in-line and an offset on the same runway. Only had markers on the in-line.

[nice castle]

Coff, beg to differ?

Runway QFU is 203 and the FAT of ILS is 208.

So, it is offset towards D141, not away from it.

My suggestion would be that this is due to the higher ground to the west of the FAT. 208 seems to coincide with the lowest of some pretty high ground.

ISTR the RADALT drops quite low when you fly this approach.

Cheers.

[clicker]

Nice Castle,

I thought that was possible but also noticed that the GP is set at 3.5 so assumed that was for the height clearance.

After your suggestion what now puzzles me is the RNAV procedure sets the inbound track nearer to one of the summit of one of the hills you mention than the ILS procedure does.

[nice castle]

Hmm. Well, there is probably more to the installation and offset reasoning than meets the eye. Yes, 3.5 deg definitely due to that ridge line. I concede that the inbound arc also tracks you directly over the high ground as well, whichever way you arrive?
But it's not D141 that drives the offset.

[nice castle]

Oh, and the RNAV approach has a very steep approach angle, recommended at 478 ft per nm, so what, about 4.5-5 degrees?

[Davita]

Good one @basil....Lagos would be very much a preferred layover than LAX.....NOT!:E

My first/last time to Lagos was on an RAF VC10 carrying the pipe smoking PM Harold Wilson....I'm still trying to forget those days.

[fireflybob]

Runway QFU is 203 and the FAT of ILS is 208.


nice castle, the runway chart I am looking at shows QFU is 214 so I agree with with coffmanstarter that ILS is offset to avoid D141.

[Trim Stab]

Oh, and the RNAV approach has a very steep approach angle, recommended at 478 ft per nm, so what, about 4.5-5 degrees?

The "ILS" at Lugano is offset and 6.65 degree. I used quotation marks because although the guidance works like an ILS it is classified as an IGS. You have to be careful to intercept the glide at a low speed and in a draggy configuration otherwise you risk being unable to stay at Vapp on the way down.

[Gulfstreamaviator]

Training take-offs involving practice engine failure will not be allowed when using Runway 03 at any time, or when using

Runway 21 when a nuclear train is passing.

That's OK then....

glf

[obnoxio f*ckwit]

Not sure BNFL or whoever they are now would be too worried about a light aircraft crashing into one of their nuclear trains:

Train test crash 1984 - nuclear flask test - YouTube (http://youtu.be/ZY446h4pZdc)

[moggiee]

I've seen a video of that HKK approach. Scary or what. Left at the flats, right at the boards. That said as I like flying I would loved to have been in a jump seat for that.
I always enjoyed flying that approach in the (recently retired) Queen of the Skies.

[Courtney Mil]

They're not nuclear, they're diesel.

[Basil]

Re HKG:
The landing would become even more challenging when crosswinds from the northeast were strong
. . and, if from the southwest and one didn't start the turn early to compensate, one would be blown through the centreline with very little opportunity to re-align :eek:

Crazy Landing at Kai Tak! - YouTube

[Basil]

Train test crash 1984 - nuclear flask test
Well, it's the driver I feel sorry for!

[Davita]

Thanks for the link Basil...crazy indeed. That was Korean Airlines and the windsock didn't look too full, but was from SW and across.

As an F/E I crewed on B707 for 4 years; 2 years on L1011 and 10 years on B747 and must have done that approach 100's of times and never had an incident...mind you...our pilots were supermen.
I know that because, in the aeroclub after landing, when we'd have a wind down drink before going home...they would often tell me so...:D:E

[chevvron]

Looking at googlemaps, it would seem there is space off the end of the runway at Lydd for an inline localiser, but it's actually situated on the south east end of the disused runway, which leads me to suspect maybe the ground to the southwest was deemed too unstable to support it. I would think it is just topsoil overlaying shingle; certainly the water table can't be too far below the surface, so using a stable well drained foundation would seem logical.
The reason offset localisers are used at Sumburgh is simple; both ends of the runway are too close to the sea for an inline one to be positioned on land!

[Basil]

in the aeroclub after landing, when we'd have a wind down drink before going home...they would often tell me so...
Only went there once or twice (wasn't there a story about the trophy prop? :E ) but used to go into a UK club after final landing of the day; very flattering but needed the Roman triumph "hominem memento te" before the next approach in crap wx ;)

[ShotOne]

While there are some interesting responses, clicker, I'm conscious that some of them have wandered away from your question. An IlLS is a precision approach which means the pilot gets guidance on glidepath and azimuth. The old Kai Tak IGS approach, for instance, wasn't an ILS approach at all; it merely used an ILS beam to allow the pilot to position for a visual landing.

In terms of your question about "kicking off" , what happens is the ILS guides the aircraft to a point (decision height) where the pilot will decide to land or goaround. For a modern airliner this might be the touchdown on the runway (CAT THREE). If the approach is offset, as at Lydd this will be higher to allow the pilot to align with the runway.

[Trim Stab]

As Shotone implies, if you couple an autopilot to an ILS and don't disconnect it at minimums, the aircraft will continue on its trajectory until it's nose wheel hits the runway piano-keys. The minimums on ILS are low (0-200ft depending on various factors) because the pilot does not need to make any configuration changes or alter the trajectory of the aircraft (except to flare) in order to complete the landing. This is why it is called an Instrument Landing System. The maximum runway non-alignment of an ILS is normally 3 degrees.

If the aircraft has to be manoeuvred visually by the pilot at minimums because the radio-beams are not aligned with the runway, then the approach is an IGS (such as Lugano which I mentioned, and the old Hong Kong approach). IGS means Instrument Guidance System. It uses the same ground and aircraft equipment as ILS, and the pilot flies it in exactly the same way as an ILS, except that at minimums he will have to visually manoeuvre the aircraft to land, and sometimes make configuration changes too (e.g. at Lugano the approach is so steep that I preferred to only select full flap once I was below minimums, aligned with centreline and on a 3 degree glidesope, even though this meant taking full flap much later than is normally sensible). The minimums of IGS are much higher to give the pilot altitude and time to correct the trajectory of the aircraft and make any configuration changes needed.

I haven't been to Lydd, but if the misalignment is 5 degrees, then possibly it should be classified as an IGS, as that would immediately flag up to the pilot the misalignment.

[chevvron]

I'm not sure which is which now, but military airfields were allowed to use a max of 5 deg offset and ICAO was max 3 deg offset (or it could have been the other way round), but I believe military airfields shifted to ICAO calculated minima about 5 years ago, so the criteria is probably the same for both now.

[ShotOne]

Good explanation trim stab but one adjustment; the ILS touchdown point is 450m along the runway not the piano keys, and even then, hopefully not on it's nose wheel.

[Davita]

I recall that ILS's were categorized depending on their accuracy. Cat1 to3C. Is it still the same?
A displaced ILS would have a higher minimum and 3C permitted autoland i.e. zero visibility.
I've been on board many autolands in practice and a few in earnest...I think Gatwick, or was it Heathrow, have autoland 3C.
The Autopilot does the flare and the auto-throttles control the thrust. The crews duty was to disengege and reverse and keep on the centre line.

Once I was a guest on a Belfast at RAF Brize Norton which I think used a leader cable system...it maintained the centre line with a roll-out mechanism of swirling horizontal mini-barbers poles which rotated at different speeds, showing which way to manouevre.
Anyone remember that system and how it worked?

[Trim Stab]

Good explanation trim stab but one adjustment; the ILS touchdown point is 450m along the runway not the piano keys, and even then, hopefully not on it's nose wheel.

No - the ILS glide path intercepts the runway at the piano-keys, so that is where the nose-wheel will hit if you do not flare.

Obviously, if you flare, you will land on your main gear further down the runway. Not sure where you get the 450m figure from though.

[Checks Complete]

Dusting off the old FI hat, I think that an instrument approach can only be an ILS if the Localiser is offset 3 degrees or less. If the offset is more than 3 degrees it becomes a localizer type directional aid (LDA) with a higher MDA/MDH. An offset ILS set up so that an aircraft on the ILS centre line and glide path crosses the extended runway centreline at DA/DH.

[Basil]

We operated the B757/767 to Cat 3C with no DH and an RVR of 75m (really just so we could see to taxi in) which brings me nicely to the leader cable idea.
We had a leader cable housing on the RAF Argosy in the sixties but never used it. I suspect trials may have been carried out but it wasn't introduced into general service. Would have been great in very poor vis with ATC monitoring ground movement radar and operating the points :}

[ShotOne]

Trim stab, sorry but that's not right. I won't argue with you here since we're digressing from the original question but the glide slope intersects 1000' down the runway and the touchdown zone is from 1000' to 3000'. If it was at the threshold as you describe, the main wheels would be in the daisies and nobody impressed.

[Trim Stab]

Yes, I meant touchdown marks, not piano-keys. Should be more careful with terminology!