SWA147 approach at LGA 23Mar24
 

This is an interesting exchange...

Southwest Boeing 737-8H4 (N8554X) performing flight SWA147 from Nashville to LaGuardia was on the second attempt to land when the aircraft suddenly deviated to the right of the approach path coming dangerously close to the control Tower at around 150-200 feet height.
Air traffic controller yelled the pilots to go around and climb immediately.

Sounds like a challenging day for all, with tailwinds, wind shear and variable RVR. Good decision to divert after two go arounds and several other aircraft doing likewise.

Based ADS-B data, aircraft passed just to the NW of the tower at a pressure-corrected altitude of 1030 ft, which would give a 790 ft vertical clearance with the 240 ft tower.

Where are the METAR's when you need them :E found the 29.79 QNH on the audio recording
My crude estimate, it's more around 700-800AGL range, concur with previous poster around 1000ftAGL, when passing abeam the tower, but already with a decent RoC.
And a Topgun style (the movie) lateral separation.
Whoever kicked the crew back into reality, did a great job!
https://cimg8.ibsrv.net/gimg/pprune....4eb0acc76a.jpg


But it's another tower I would be more worried about (although this one, most likely, had no people residing in it).
They were really aiming for 'The Korean Church of Queens' with its 60ish feet tower+cross, with a positive RoC only just about to kick in.
And laterally, within a wingspan or so... even too close for Maverick
https://cimg3.ibsrv.net/gimg/pprune....ba1992ab18.jpg

Detailed analysis
Scary

Just throwing this out there. The ILS to Rwy 4 at LGA has a note on the approach plate prohibiting auto-pilot coupled approaches. Hence the pilot was hand flying, which could explain why they got so far off the localizer course. Challenging weather for a hand flown approach. Hopefully the most experienced pilot was the one flying it.

Say what? There is no excuse for being so far off the localiser or G/S if you are flying manually.

By the time they were abeam the app.lights, they were some 9+degrees off localiser centerline, approx. 450m from the centerline
And only just about to start the G/A (some 400ft above rooftops)

Many companies have formalized limits for pilots when it becomes mandatory to stop pushing and go around. Am I wrong to suppose SWA has those too, namely after skidding over at Burbank twice? That's a lot of practical experience.

The other thing that springs to mind, long lost information from the ATPL books, is that LLZ 1 dot deviation at RWY THR marks the physical runway edges. Thus LOC antenna placement (in terms of distance behind the THR) is defined by the spread angle and the sideline anchor points for 1 dot at THR.

Any armchair investigator can take Google maps now (or AIP data from US equivalent), locate the antenna and draw the protection area of 1 dot LLZ. In general I believe, again - ready to be re-educated -, 1 dot LLZ marks the acceptable range of being "on course" i.e. within the qualified lateral protection zone to follow the GP.

Besides the deviation, low height AGL, etc, it is another interesting non standard R/T , luckily the go around and climb "order" by the TWR was performed by the right aircraft.

Localizer is 700 feet wide at threshold, standard.

Long and wide, short and skinny, both adjusted to 700 feet wide. Third of a dot is autoland limit on my jet. That's 58'. On visuals, SOP is lateral confines NLT 200'.

A good read-

https://code7700.com/ils.htm#section3

Another situation where the CVR will have been recorded over with the flight having diverted. I assume that the crew has been interviewed.

The video discussion posted by bean above details the reason that the LGA ILS 4 approach is not to be a coupled approach. There was a small hotel built off of the approach end of runway 4 which interferes with the GS signal. This was discovered back about 10 years ago by the FAA technical division after test flights.

So here's my question... if the GS signal is degraded to the point that modern autopilot can get spurious information, then why is the information provided by the GS valid for a hand flown approach?

I think it's time of the NY Port Authority, the FAA and the airlines to buy the Avion Hotel and tear it down!

The ILS 04 has always been a troublesome approach, going back decades. An FAA DC-3 Flight Check crashed testing back in the early ‘70s. Lots of buildings, hangars, the piers all make it problematic. The mins used to be about 400-1, now they’ve figured out a way to get them slightly lower. When it was 400-1, the reported weather would be 200 or 300 and mile, everybody would be getting in. An old squadron mate who was a B727 captain at the time told me it was “the most cheated on approach in the country”.

Of course, ceiling wasn’t governing, but it is indicative.

Excellent, and Code7700 is so great I actually wanted to send a greeting tk the author the last week, just for appreciation. Hoping the rumors are not true.

I interpret half-scale to be 1 dot out of 2 on my ship.

However that cannot be pinpointed to RWY edge if the full LLZ beam 2.5 is 700 feet wide.

​​Noted. For a 60m wide runway it does come reasonably close to pavement edge at least.

So I am truly curious about this...from the ILS approach plate runway 4 KLGA..."Autopilot couple approach NA."

So I ask again... if an ILS GS signal isn't good enough for the electronics, why is it good enough for a hand flown approach?

Because the deviations are very transient and happen quickly so the pilot won't notice them (or if they do, they'll average them out).

An autopilot would instantly jump on each one of those deviations.

I've not done that approach myself, but that's how it was explained to me by someone that has.

Same reason some approaches are legal for autoland and some are not.

There is quite a few ILSs that must be hand flown Monterey, CA for one.

False ILS
 

As an ex Radio Engineer, the fact that he was quite a bit to the right of the Hotel, suggests he was following a False ILS Signal. This would be produced by diffraction of the ILS Signal. Effectively the hotel was broadcasting it's own ILS signal, because of the reflective nature of the components of the hotel construction.