PPRuNe Forums - Offset ILS Cat 2

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B737-pilot

19th Sep 2011 07:57

Offset ILS Cat 2

Hello.
At the end of August a new temporary chart was published for LRBS ILS 07. The new final approach course is 069. Runway heading remained the same 070 degrees. Minima is 100ft RA and RVR 300 m.

Note: Boeing states in the FCM that autoland shouldn't be attempted if the final approach is differnt from the runway heading.

QUestion: Is it legal/ possible to fly a coupled single channel down to the minimums, followed by a manual flare and landing? Should an increment to the minimums be made?

Thanks for your help !

esreverlluf

19th Sep 2011 08:43

C'mon - it's only 1 degree. Probably a rounding error each way. There are many airports around the world where autoland is permitted with a 1 degree difference between QDM & LOC heading.

Haven't seen any autoland runways with greater than 1 degree though.

Interestingly, the wording in my 744 FCTM is slightly different and says

"Autoland should not be attempted unless the final approach course path is aligned with the runway centreline. If the localiser beam is offset from the centreline the AFDS ROLLOUT mode may cause the aircraft to depart the runway."

Also - not sure about the 737, but should you be flying to Cat II minima with a single autpilot engaged? Might be a 737 thing, but in my experience on 767 and 744 you would have at least 2 autopilots engaged for Cat II minima.

punk666

19th Sep 2011 08:45

Is it legal/ possible to fly a coupled single channel down to the minimums, followed by a manual flare and landing? Should an increment to the minimums be made?

Not all landings are autoland my friend..so the answer is yes to your question, pilots do fly the plane :E

Any final course within 30 degrees of the runway heading is classed as a straight in approach (FAA).

bfisk

19th Sep 2011 11:14

Quote:

Any final course within 30 degrees of the runway heading is classed as a straight in approach (FAA).

But straight-in is opposed to circling, not opposed to offset, which was in question.

Cough

19th Sep 2011 12:03

Many aircraft manual land from a CAT II autopilot controlled approach, ie. ATR, 146.

However, if you haven't been trained in a Cat II ManLand, then you shouldn't - You would be stepping outside your operators approval...

aterpster

19th Sep 2011 17:14

punk666:

Quote:

Any final course within 30 degrees of the runway heading is classed as a straight in approach (FAA).

Not exactly. That is the case for VOR, NDB, and LDA.

15 degrees is the maximum for RNAV (LNAV or LP only) for CAT C and D.

CAT I ILS is limited to a 3 degree offset.

CAT II and III, zero offset.

Because the runway magnetic bearing sources used by chart makers can be less than sterling, we got the FAA to publish the actual offset of any ILS by the exact amount.

For ILS Jepp publishes the official offset in the ILS frequency box.

For RNAV with vertical guidance and RNP AR the offset is published in the briefing strip. RNP AR with any amount of RF legs in the final segment is not permitted any offset.

Can't speak for the myriad iterations of PANS-OPS. There is no substitute for a good airline technical department that has direct access to all of the aviation authorities for destination airports.

Avenger

19th Sep 2011 18:25

AS observed there are many airports where there is a degree change between heading and course. At minima of 100 ft, how much off the centre line is a 1 degree offset when the ILS Antenna is 300m in! considering the autoland criteria can be xx metres either side of the centreline for certification I think this is not an issue.

safetypee

19th Sep 2011 20:00

Avenger, the LOC antenna might be > 6000ft away at the far end of the runway, thus the offset might be significant.
However, the accuracy issue is the physical offset between the LOC alignment and the runway direction, not the reported direction. Thus if the antenna is in the correct position – runway centerline, and the beam centre is ‘electronically’ stable, then there shouldn’t be many problems.

mustafagander

20th Sep 2011 01:15

Anyone looked at LHR 27 runways recently? No way the QDM is 271.

reynoldsno1

20th Sep 2011 03:17

The course/headinngs will be determined by adding/subtracting magnetic variation to the great circle bearing calculation.

The final course calculation and runway bearing calculations will result in different great circle true bearings, and slightly different variation values - rounding can result in different values.

Howeve, I agree that a degree (excuse pun) of pragmatism needs to be applied, and the course/headings should be adjusted to the same value - if only to cut down the number of 'phone calls and forum threads....:eek:

9.G	22nd Sep 2011 01:33

that's for the airbus:

Quote:

AUTOMATIC LANDING WITH OUT-OF-DATE ADIRS MAG VAR TABLE
Some Airbus SA and LR aircraft continue to fly a number of years with ADIRS part numbers fitted with out-of-date magnetic variation tables. If the ADIRS magnetic variation differs by more than 2 ° or 3 ° (depending of aircraft type) compared to the airport current magnetic variation, the lateral performance of the automatic landing and rollout is significantly affected, which prevents from using the automatic landing system on these airports. Airbus publishes in the FCOM for each year, the list of airports where automatic landing is no more authorized with these ADIRS part numbers.

Seen that numerous times with 1 degree difference between the chart and the box and performed on those RWY's autolands without problems. :ok:

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