False LOC capture
Thread Starter
Join Date: Feb 2001
Location: Milkway Galaxy
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
False LOC capture
In internet there are lots of articles and documents about False Loc Capture, but not a single clear image what pilot may see at the time of its occurrence.
The image is my guess, do you consider it is correct?
The image is my guess, do you consider it is correct?
Moderator
By its very nature, a trap.
That's why one is better placed to position by other aids to a point where one knows that the aircraft is on, or very nearly so, the localiser.
That's why one is better placed to position by other aids to a point where one knows that the aircraft is on, or very nearly so, the localiser.
Only half a speed-brake
]The indications on flightdeck are absolutely normal. Except the LOC is not supposed to be there.
Actually, it is. The signal is a side-lobe from the antenna, which is there due to the electronic design of the NAV-AID.
Your picture shows A/C's track similar to final approach course - it is possible if you are flying parallel to the landing direction, but then the "false" loc would steer you towards the antenna, approx 35 degrees in a different direction.
Most likely occurence is:
- on a base leg heading, approximately 35 degress off the final track
- close to the field (12 NM or less)
- significantly below gentlemenlike profile (around 2500 ft aal or lower)
last experience here at 2000 AAL:
falselocVNO.png
Actually, it is. The signal is a side-lobe from the antenna, which is there due to the electronic design of the NAV-AID.
Your picture shows A/C's track similar to final approach course - it is possible if you are flying parallel to the landing direction, but then the "false" loc would steer you towards the antenna, approx 35 degrees in a different direction.
Most likely occurence is:
- on a base leg heading, approximately 35 degress off the final track
- close to the field (12 NM or less)
- significantly below gentlemenlike profile (around 2500 ft aal or lower)
last experience here at 2000 AAL:
falselocVNO.png
Join Date: Apr 2005
Location: Dubai
Posts: 348
Likes: 0
Received 0 Likes
on
0 Posts
I would agree with FD, I had this a few years ago on a training trip into Doha with an A330. We were 15 nm 90 degree right base for 34 and ATC cleared us for the approach. Trainee reached up and hit the APP button just as i noticed the LOC index about 1/4 dot fly left. Aircraft immediately went LOC* and I took control pulling heading and resetting the right base trajectory we were on originally (poor trainee didn't know what had happened, bit of startle and surprise). I would suggest that to show the whole picture, you would need to have the ND up as well. The LOC index would be in the middle with (maybe, probably) a different heading to the LS course index. (unless it was paralleling as per FD above - see Resolute Bay as an slightly adjacent example).
Moderator
The indications on flightdeck are absolutely normal
Indeed. Some years ago, on a contract sim training exercise with SAA, their 732 box did a very nice false indication for one of the aerodromes. Needless to say, I set folk up to see it happen.
Hence my suggestion that one should use something else to position in the right place before getting excited by the ILS. Once folk see how it can sucker them in, the message sinks in nicely.
Trainee reached up and hit the APP button
Another trap. The better sequence is
(a) get on or approaching the localiser by other means, then select LOC - avoids a false course problem
(b) approaching the correct distance for the glideslope, then select GS - avoids a false slope problem .. although the VSI tells the story before things get interesting. Obviously, with a functioning DME, this shouldn't catch anyone out.
We never trusted our lives totally to a bunch of electrons .. Anything to avoid excitement in the aeroplane ..
Indeed. Some years ago, on a contract sim training exercise with SAA, their 732 box did a very nice false indication for one of the aerodromes. Needless to say, I set folk up to see it happen.
Hence my suggestion that one should use something else to position in the right place before getting excited by the ILS. Once folk see how it can sucker them in, the message sinks in nicely.
Trainee reached up and hit the APP button
Another trap. The better sequence is
(a) get on or approaching the localiser by other means, then select LOC - avoids a false course problem
(b) approaching the correct distance for the glideslope, then select GS - avoids a false slope problem .. although the VSI tells the story before things get interesting. Obviously, with a functioning DME, this shouldn't catch anyone out.
We never trusted our lives totally to a bunch of electrons .. Anything to avoid excitement in the aeroplane ..
Only half a speed-brake
re (a)
that technically sound advice may not be the best practice under some scenarios. Think closely spaced parallel runways, or tight airspace and slightly overloaded crew.
I find it harder to discover IN TIME that the aircraft did not turn as opposed to turning early when unexpected (with an FMA change).
that technically sound advice may not be the best practice under some scenarios. Think closely spaced parallel runways, or tight airspace and slightly overloaded crew.
I find it harder to discover IN TIME that the aircraft did not turn as opposed to turning early when unexpected (with an FMA change).
Moderator
To clarify .. my suggestion involves monitoring the ILS indications throughout to avoid the concerns you cite. Autoflight, of course, should be used as appropriate to workload.
Why not brushing up and study the limitations of the localiser beam??
And while you are at it, take the glide slope beam as well........
And yes, those limitations may be further restricted in notams etc.....
And while you are at it, take the glide slope beam as well........
And yes, those limitations may be further restricted in notams etc.....
Airbus caution against arming approach outside the ICAO envelope of normal capture - +/- 8 deg of ILS track, and within 0.3-1.75 times the GPA.
Only half a speed-brake
cs: reference please 
In PRO-NOR-SRP-01-70 ILS/MLS/GLS/FLS Approach it is not.
My training and was simple, definitely not to delay arming the APP mode until inside the ICAO envelope, or after "almost there" verification was made using other means.
Cleared for ILS approach -> press the button UNLESS in akward position. No need to wait even for angle to be less than 90 deg (737 habit - but I still do) .
. follows the philosphy "what's cleared (ATC) is set (autopilot modes)"
. reduces workload later and removes errors of omission
. IF you manage to hit and lock on a side-lobe, then ND and FMA gives clear picture of what has happened and corrective action is one pull of a knob.
Or, in other words: "When cleared by ATC and when appropriate" (this is FCOM PRO-NOR-SRP-01-70 ILS/MLS/GLS/FLS Approach)
In PRO-NOR-SRP-01-70 ILS/MLS/GLS/FLS Approach it is not. My training and was simple, definitely not to delay arming the APP mode until inside the ICAO envelope, or after "almost there" verification was made using other means.
Cleared for ILS approach -> press the button UNLESS in akward position. No need to wait even for angle to be less than 90 deg (737 habit - but I still do) .
. follows the philosphy "what's cleared (ATC) is set (autopilot modes)"
. reduces workload later and removes errors of omission
. IF you manage to hit and lock on a side-lobe, then ND and FMA gives clear picture of what has happened and corrective action is one pull of a knob.
Or, in other words: "When cleared by ATC and when appropriate" (this is FCOM PRO-NOR-SRP-01-70 ILS/MLS/GLS/FLS Approach)
Join Date: Dec 1999
Location: In my own little world
Posts: 1,475
Likes: 0
Received 4 Likes
on
1 Post
FCOM
PRO-NOR-SRP – Systems Related Procedures
PRO-NOR-SRP-01 – FMS
LOCALIZER (LOC) BEAM CAPTURE
The flight crew must always monitor the capture of a LOC beam. During this evolution, the PFD and ND must indicate that associated deviation indications move toward the centre of the scale. To avoid performing a false capture, the flight crew must be careful not to arm the LOC too early.
The following graph shows the angle of interception versus distance to the runway threshold that ensures that the aircraft will not overshoot the axis by more than one and a half dot.
The capture begins when the deviation is two dots or less. It is programmed to line the aircraft up on the beam with a single overshoot, even if the intercept angle is large.
Note: ICAO requires LOC beam to ensure a normal capture within 10 NM and plus or minus 35 ° from the course centerline. Some ILS systems just meet the requirement and are subject to false capture outside these limits.
PRO-NOR-SRP – Systems Related Procedures
PRO-NOR-SRP-01 – FMS
LOCALIZER (LOC) BEAM CAPTURE
The flight crew must always monitor the capture of a LOC beam. During this evolution, the PFD and ND must indicate that associated deviation indications move toward the centre of the scale. To avoid performing a false capture, the flight crew must be careful not to arm the LOC too early.
The following graph shows the angle of interception versus distance to the runway threshold that ensures that the aircraft will not overshoot the axis by more than one and a half dot.
The capture begins when the deviation is two dots or less. It is programmed to line the aircraft up on the beam with a single overshoot, even if the intercept angle is large.
Note: ICAO requires LOC beam to ensure a normal capture within 10 NM and plus or minus 35 ° from the course centerline. Some ILS systems just meet the requirement and are subject to false capture outside these limits.
Only half a speed-brake
Thanks, I do. In practical terms, if more than 45 deg off (glance at ND) it's "eeeh, wait a little shall we?" for me.
Anybody have the books at hand, to show what is the offset angle of the dominant side-lobe? I did a quick serch but to no avail.
Anybody have the books at hand, to show what is the offset angle of the dominant side-lobe? I did a quick serch but to no avail.
FCOM-PRO-NOR-SOP-18-C-approach using LOC GS guidance
"ICAO defines the envelope where the quality of the G/S signal ensures a normal capture. This envelope is within 10 NM, ±8 ° of the centerline of the ILS glide path and up to 1.75 θ and down to 0.3 θ (θ = nominal glide path angle). When arming the approach well outside of the normal G/S capture envelope, a spurious G/S* engagement may occur due to a wrong G/S deviation signal. Whenever the pilot notices the pitch movement, or the spurious G/S*, or the trajectory deviation, he will immediately disconnect the AP, if engaged, to re-establish a normal attitude and will disengage APPR mode. It is then recommended to arm/rearm APPR (ILS) mode within the normal capture zone."
"ICAO defines the envelope where the quality of the G/S signal ensures a normal capture. This envelope is within 10 NM, ±8 ° of the centerline of the ILS glide path and up to 1.75 θ and down to 0.3 θ (θ = nominal glide path angle). When arming the approach well outside of the normal G/S capture envelope, a spurious G/S* engagement may occur due to a wrong G/S deviation signal. Whenever the pilot notices the pitch movement, or the spurious G/S*, or the trajectory deviation, he will immediately disconnect the AP, if engaged, to re-establish a normal attitude and will disengage APPR mode. It is then recommended to arm/rearm APPR (ILS) mode within the normal capture zone."
Only half a speed-brake
G/S is a different animal. On the type for which we hijacked the thread, G/S won't engage until LOC is active. Thank you too still, I did look in NOR SOP before asking that of you, but missed.
Thread Starter
Join Date: Feb 2001
Location: Milkway Galaxy
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for replies, but I guess still nobody so sure what may be on PFD
FD,
Sorry, but I couldn't get what you mean.
On the Image what I attached, RA 270 and DME is 1.0.
If we ignore those and assume airplane is at , let's say 1500 RA and 5 DME, I guess that image represents an airplane (let's say Airbus) Auto flight System turned the airplane near parallel to front course (145 degree) at a point quite offset from Localizer track, however as get close, airplane is drifting to LOC antenna.
Any clear objection ?
FD,
last experience here at 2000 AAL:
On the Image what I attached, RA 270 and DME is 1.0.
If we ignore those and assume airplane is at , let's say 1500 RA and 5 DME, I guess that image represents an airplane (let's say Airbus) Auto flight System turned the airplane near parallel to front course (145 degree) at a point quite offset from Localizer track, however as get close, airplane is drifting to LOC antenna.
Any clear objection ?
Last edited by JABBARA; 5th Apr 2017 at 23:39.
I've had false LOC capture a couple of times and now delay arming the approach until quite late.
A few points worth noting:
1. Within 20nm of the threshold LOC capture takes over from NAV and the aircraft will deviate slightly off route to intercept. Some controllers don't like this if you have been cleared to a waypoint less than 20nm away from the runway and from there, cleared ILS approach.
2. No French manufactured or registered aircraft can descend on the glide path before it has captured the localiser. LOC* doesn't mean you are within those limits and you can overfly the glideslope if you are very close and the system hasn't decided to let you descend. Monitor closely and be prepared to go V/S once on the LOC and if the G/P is underneath you.
3. Extended runway centreline with NAV blue can be useful if cleared for the approach outside of the protected area. You will line up with the runway if you forget to arm the APP rather than fly through into high terrain or a parallel runways approach path.
4. Check that the FMS hasn't calculated a hold if you are cleared to a waypoint for ILS intercept with a large angle. 90' intercepts are used at some airports and a hold can appear at the waypoint.
5. FCOM has a chart showing distance/speed/angle where an ILS can be intercepted.
A few points worth noting:
1. Within 20nm of the threshold LOC capture takes over from NAV and the aircraft will deviate slightly off route to intercept. Some controllers don't like this if you have been cleared to a waypoint less than 20nm away from the runway and from there, cleared ILS approach.
2. No French manufactured or registered aircraft can descend on the glide path before it has captured the localiser. LOC* doesn't mean you are within those limits and you can overfly the glideslope if you are very close and the system hasn't decided to let you descend. Monitor closely and be prepared to go V/S once on the LOC and if the G/P is underneath you.
3. Extended runway centreline with NAV blue can be useful if cleared for the approach outside of the protected area. You will line up with the runway if you forget to arm the APP rather than fly through into high terrain or a parallel runways approach path.
4. Check that the FMS hasn't calculated a hold if you are cleared to a waypoint for ILS intercept with a large angle. 90' intercepts are used at some airports and a hold can appear at the waypoint.
5. FCOM has a chart showing distance/speed/angle where an ILS can be intercepted.
Join Date: Jan 2015
Location: Sky
Posts: 78
Likes: 0
Received 0 Likes
on
0 Posts
Hello guys
We have faced with such situations too.As usual it have happened on the airport with old equipment (north airports "for Russian users only" like USMU,USNN,UOOO and airports of the former USSR Asia's republics UCFM,UCFO,UTDD) false LOC as well as false G/S
There's some tips ,don't forget about bearing from OM,and distanse from DME if available
I have never faced it in Asia or Europe.
We have faced with such situations too.As usual it have happened on the airport with old equipment (north airports "for Russian users only" like USMU,USNN,UOOO and airports of the former USSR Asia's republics UCFM,UCFO,UTDD) false LOC as well as false G/S
There's some tips ,don't forget about bearing from OM,and distanse from DME if available
I have never faced it in Asia or Europe.