YMMB DIsplaced Thresholds - What the?

[Sunfish]

Noticed the displaced thresholds on every runway at YMMB in the latest ERSA.

Pardon me for showing my ignorance, but why?

Is it permissible to land short of the displaced thresholds? The party trick with the Sportstar was to land as short as possible and make the first taxiway on 17L

[Robdog]

Im not sure why the thresholds are displaced but I do know you cannot land short.

[Fieldmouse]

Sunfish, since no-one else has had a go yet I'll try despite never having been to YMMB. Airservices has been updating ERSA with pictorial representations of displaced thresholds for a couple of years now. Tghe ones at Moorabin I have in a 2010 issue but not in a 2008 even though the thresholds were displaced back then too. Lots of reasons for displaced thresholds and the devil is in the distances supp of ERSA. Lots of fairly steep climb out gradients there which translate into displacements on the reciprocal runway depending upon the standard to which the runway is surveyed. Non instrument code 1 requires a 5% clear approach, code 2 a 4% clear approach, code 3 a 3.33% clear approach etc. What won't show up in the distances supp is an allowance for a critical transient vehicle on a road in the undershoot. Where I am the new rules on stock truck size meant we have to allow over 6% in one of our approaches over the highway. A bit pointless for a lighty coming in on a steep approach but aviation regs are a one size fits all deal. As for landing before a displaced threshold? Since the displaced area is included in the TORA it's guaranteed safe so why not. As long as nothing bad happens. Then there might be some explaining to do.

[clark y]

Sunfish,

No idea about YMMB, but I think Fieldmouse is probably correct about the airport being resurveyed for obstacles. Sometimes it could just be that some trees have grown up within the runway splays.
As for the practice of landing short, I think it is a habit that should be avoided. It might seem safe at YMMB but there are airports where the obstacle on short final can be a real threat to life, and quite often unseen. i.e. powerlines.


Fly safe.

Clark y.

[john_tullamarine]

The usual reason for a displaced landing threshold is to preserve the required obstacle clear approach surface according to the runway categorisation. For some runways this can involve a significant loss of declared LDA.

The declared distance should be used for operational calculations. The intention is that the aircraft doesn't land short of the markings and the pilot exposes himself/herself to censure if doing so leads to any problems.

The opposite direction TORA may well extend into the area prior to the commencement of the declared LDA.

The party trick with the Sportstar was to land as short as possible and make the first taxiway on 17L

I have no idea what the Sportstar might be but that particular party trick is a good way to end up embarrassed in the event of a cessation of noise .. yes, I know, we all did it as youngsters.

[OZBUSDRIVER]

Could I be so facetious to suggest.....the prevalence of airline style flat approaches has precipitated the need to displace thresholds to ensure clearance above vehicular traffic.:E

[VH-XXX]

the need to displace thresholds to ensure clearance above vehicular traffic

If that's the case then Tyabb should displace their threshold by 300 metres!

[Lasiorhinus]

YPJT, thats Moorabbin, YMMB, and has permanently displaced thresholds. Melbourne is YMML, and doesnt have displaced thresholds (at least it didnt when I was last there).

The displaced thresholds for Moorabbin are precisely because of obstacles that would otherwise infringe the splays. You're more than welcome to use the full length of the runway including before the threshold for takeoff, but landing must be made after the displaced threshold. ERSA RDS shows quite different figures for TORA and LDA.

[YPJT]

Thanks Lasiorhinus,

I feel like such a ****!
:O

[ReverseFlight]

Actually it makes sense. I've always hated the tree(s) before the threshold of 35R and it doesn't help when students tend to almost land on the factory rooftops and then "drag" themselves in horizontally until Lower Dandenong Road.

[baswell]

I have no idea what the Sportstar might be but that particular party trick is a good way to end up embarrassed in the event of a cessation of noise .. yes, I know, we all did it as youngsters.
I do that party trick at other airfields in my SportStar. Spot landing / short landings must be practised regularly anyway!

This is not your daddy's Cessna.

To perform it properly, you do a steep descent with full 50 degree parachute (otherwise known as flaps), the engine very close to, if not at, idle, at what would otherwise be just about your clean best glide.

If the noise, which you were not using anyway, stops, you put your flaps away and probably end up landing halfway down the runway.