Landing before a displaced threshold

[nightbird]

Would you land before a displaced threshold (touch down on the white arrows)? Why?

[Beefitarian]

Not intentionally. It's an unknown surface. Could be fine or maybe there is a nasty pot hole, a piece of asphalt might break, shift or sink when you touch down on it. You can't really know much about it except, instead of fixing or maintaining that surface they just painted markings to tell you not to land on it.

[Whiskey25]

From the TC AIM

[quote]3.3 Displaced Runway Threshold

Occasionally, natural and human-made obstacles penetrate the obstacle limitation surfaces of the take-off and approach paths to runways.

To ensure that a safe clearance from these obstacles is maintained, it is necessary to displace the runway thresholds. In the case of runways for which instrument approach procedures are published in the CAP, the usable runway distances for landings and takeoffs are specified as declared distances. The displacements are also depicted on the aerodrome or airport diagram in both the CAP and the CFS. For other runways not having published CAP approaches, the requisite data is given in the CFS. Where a threshold is displaced, it is marked as shown in AGA 5.4.1.

When the portion of the runway before the displaced threshold is marked with displaced threshold arrows (see AGA 5.4.1), it is permissible to use that portion of the runway for taxiing, for takeoff and for the landing roll-out from the opposite direction. In addition, this displaced portion of the runway may be used for landing; however, it is the pilot’s responsibility to ensure that the descent path can be safely adjusted to clear all obstacles. When taking off from the end opposite to the displaced threshold, pilots should recognize the fact that there are obstacles present that penetrated above the approach slope to the physical end of the runway, which resulted in the threshold being displaced.

When a section of a runway is closed, either temporarily because of construction or permanently because the full length is no longer required, the closed portion of the runway will not be available for the surface movement of aircraft for taxiing, take-off or landing purposes and is marked with an “X”, indicating that the area is not suitable for aircraft use.

The closed portion of the runway may be shown on the aerodrome or airport diagram in the CFS and the CAP for identification purposes; however, declared distances will only include runway length starting at the new threshold position./quote]

If you are talking about arrows on a stopway, you can't land on it. A stopway isn't the same as a displaced runway. Oh and BTW, I wouldn't do it in the U.S though, you're not allowed.

[Beefitarian]

Huh, well then. I guess I was wrong. Why is it different in the us?

[Whiskey25]

In the U.S. you are only authorized to use the displaced portion for the take-off and landing rollout,. To be honest I'm not 100% sure as to the reason why other than regulatory differences.

From the FAA AIM:

2. Displaced Threshold. A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction. A ten feet wide white threshold bar is located across the width of the runway at the displaced threshold. White arrows are located along the centerline in the area between the beginning of the runway and displaced threshold. White arrow heads are located across the width of the runway just prior to the threshold bar, as shown in FIG 2-3-4.

I think the cases you mentioned ref the landing surface would result in a portion of the runway being closed and marked appropriately.

[ahramin]

Absolutely I would, it's perfectly usable pavement. But it's not often that there is a reason favoring it. Typically the extra runway is only useful when you are flying a higher performance airplane, in which case you are likely going to want to aim for the displaced threshold anyway because you want the terrain clearance. In a small airplane when you don't need the terrain clearance, you likely don't need the runway either.

But if I'm in a light aircraft and there's an advantage to using the entire runway, I'll use it.

[Tim]

whiskey, the AIM is not a regulatory publication, i.e. the things written in it are not law unless it refers you to the CARs.

ive done it and seen it done countless times at glider & tow plane operations. i wouldnt do it on my first time into a new airport, and as ahramin said, it would be a light aircraft thing only.

[CpnCrunch]

Huh, well then. I guess I was wrong. Why is it different in the us?

Actually, you're sort of right. I learned to fly at Stapleford in the UK, and there was a displaced threshold on grass runway 19...I'm pretty sure the reason given to me was because the ground was too soft for landing on, but fine for taxiing. Also, if you look up "displaced threshold" on wikipedia, it says:

"A displaced threshold may also be introduced if a beginning section of the runway is no longer able to sustain the continuous impact from landing aircraft. In such a case, aircraft are expected to land beyond the displaced threshold. Departing aircraft are permitted to use the displaced section of the runway for takeoffs or landing rollouts because those aircraft are not impacting the runway with the force of a landing aircraft"

Interestingly, the wikipedia reference for that statement points to the tc.gc.ca website, but it doesn't mention anything about "no longer able to sustain the continuous impact from landing aircraft" (and in fact says you are ok to land if there are no obstructions).

I think in the UK (and perhaps other countries) you shouldn't land on the displaced threshold, but apparently it is ok in Canada.

[Colonel Sanders]

I have a little experience with this. In Canada, trees grow
vertically up. Sometimes they grow up into areas not
permitted for certified runways, on short final.

So until the trees are trimmed, the runway threshold is
temporarily displaced with some white paint, notam,
etc. This is very common. IIRC CYGK has rwy 01
displaced right now. CYOW rwy 04 is permanently
displaced. etc.

The idea is that you as a pilot get your guaranteed
obstacle clearance if you aim for the displaced threshold.

If it's day VFR and you're willing to risk your 172 exploding
during a slip with flaps, have at 'er with a steep approach.

Another temporary obstacle might be a crane. If some
weenie puts up a tower in the wrong place, the displaced
threshold can become permanent.

I figger if you can use it for takeoff, you can use it for
landing. At your own risk.

[trampbike]

If it's day VFR and you're willing to risk your 172 exploding
during a slip with flaps

An instructor once told me that slipping close to the ground was not a good thing, in fact that it was dangerous, because it could induce a spin. The guy was wearing a suit with epaulets, he must have been right...


About the diplaced threshold, why aren't there two different kinds of markings (one type for the displaced threshold for obstacle clearance and the other type for the runways in bad condition).

[lilflyboy262]

I could see why an instructor would tell you that. A newby pilot who could quite easily get slow and stall/spin.

I'm pretty sure its the same in NZ. You cannot land on a displaced threshold, but you are allowed to use it for taxi and takeoff. To be honest, I have never had a field that was so short that a displaced threshold made a difference on landing, so why not just land after it?
Unless you are trying to make taxiway alpha....

[ahramin]

risk your 172 exploding during a slip with flaps

Boy does that bring back some memories.

[trampbike]

I could see why an instructor would tell you that. A newby pilot who could quite easily get slow and stall/spin.

A slip is very anti-spin.
Roll and yaw are opposed.

[ahramin]

I could see why an instructor would tell you that. A newby pilot who could quite easily get slow and stall/spin.

A slip is very anti-spin.
Roll and yaw are opposed.

Please tell me you don't fly planes for a living (or over populated areas).

[Doc]

Runways are displaced for a reason. Since I don't know that reason, I abide by the displacement. It could well be for uneven ground/rough surface conditions/frost heaves etc. Take off is a different "sport" altogether, I can taxi out and "inspect" the area.

[V1CUT]

5.2.4.11 Standard - Where a runway threshold is permanently displaced arrows conforming to Figure5-4 shall be provided on the portion of the runway before the displaced threshold except that:

when the portion of the runway is unfit for the surface movement of aircraft, closed markings as described in 7.1.1 shall be provided; or when the portion of the runway is intended to be maintained as a stopway, chevron markings as described in 7.3.1 shall be provided.
5.2.4.12 Standard - When a runway threshold is temporarily displaced from the normal position, it shall be marked as shown in Figure5-4. All markings prior to the displaced threshold shall be obscured and the runway centre line marking converted to arrows except that when the portion of the runway is unfit for the surface movement of aircraft, closed markings as described in 7.1.1 shall be provided.

Note - In the case where a threshold is temporarily displaced for only a short period of time, markers in the form and colour of a of a displaced threshold marking may be used, rather than attempting to paint this marking on the runway.

[Colonel Sanders]

As long as no one slips with flaps, everything will be ok.

[Jastapilot]

If I had a 'need', as in an emergency, I wouldn't hesitate to use the extra runway. Otherwise I can't see 'needing' that extra length, so I will land past the threshold.


As for exploding 172's... never heard that one before! Exploding because of a slip??

[Beefitarian]

They usually only explode if you have the flaps down. A regular slip will just induce a spin.

[Colonel Sanders]

**** Humour Alert ****

172's actually hardly ever explode, even if you slip them with flaps.

That is all. Carry on,

[CpnCrunch]

There seems to be some confusion about stall/spin as a result of slipping. I admit I'm not expert, and I just had to do a little googling to figure it out in my own head.

The confusion arises because both skidding turns and slips involve crossed controls.

As I understand it:

- slipping carries no more risk of stall/spin than normal straight-and-level flight, providing you don't slip with full flap (if prohibited), and providing you watch your airspeed.
- skidding turns will increase your stall speed the same as a co-ordinated turn (basically your load factor increase).
- skidding turns will also increase the risk of entering a spin if you enter the stall, due to the fact that the plane is yawing about its axis (the fact that you have your foot on the rudder does not increase the spin risk).

So, slipping is fine, but skidding is bad (unless you're doing aerobatics). Also, steep turns aren't really much safer than skidding turns at low level, because you're still increasing your load factor and your stall speed (which isn't a good idea when your speed is low anyway!)

Feel free to correct if I have anything wrong.

[Colonel Sanders]

steep turns aren't really much safer than skidding turns at low level, because you're still increasing your load factor and your stall speed

Minor note ....

Steep turns get a bad rap. Everyone is terrified of them because
they learned in groundschool that they are likely to stall/spin out
of them because of the increased load factor.

However. The load factor (G) only increases if you try to maintain
altitude, AND keep the ball in the center.

If you do not try to maintain altitude, you can do a steep turn with
a very low load factor. Zero, in fact. This means that the wings
aren't working very hard, and specifically, you won't have a very
high angle of attach.

I will frequently do a 90 degree banked sideslip on short final
to lose altitude (yes, completely legally. I have paper for that).

During this maneuver, the G is not infinite, because I am not
trying to maintain altitude, and the ball is not in the center. In
fact the AOA is quite low - the stall warning horn is NOT on.

One last point ... as a rule of thumb, slips are good, skids are bad.

Slips are caused by too much top (or outside) rudder. Ball
goes into the center of the turn. This is safe.

Skids are caused by too much inside (or bottom) rudder.
Ball swings to outside of turn. This is NOT safe because
the inside wing is slowed down, and is at a greater AOA
than the outside wing, which is sped up by the skid.

If you stall the inside wing with a skid, you can flip upside
down during a spin entry. Most people don't think that's
very much fun, either turning final, or shortly after takeoff.

Remember, slips are good (top rudder), skids are bad (inside rudder).

The problem is that people sometimes nudge the inside
rudder, and don't even know they are doing it, to speed
up the rate of yaw (often caused by a tailwind on base).

They are trying to keep their angle of bank down, which
is silly. You can see bank. You often can't see yaw - see
illusions created by drift.

Back to the deep fryer.

[5x5]

If it's day VFR and you're willing to risk your 172 exploding
during a slip with flaps

Slipping with flaps - when will they ever learn!

[Edelweiss air]

If it's day VFR and you're willing to risk your 172 exploding
during a slip with flaps

An instructor once told me that slipping close to the ground was not a good thing, in fact that it was dangerous, because it could induce a spin. The guy was wearing a suit with epaulets, he must have been right...


About the diplaced threshold, why aren't there two different kinds of markings (one type for the displaced threshold for obstacle clearance and the other type for the runways in bad condition).

There are two different types of displacement markings. One is the standard white arrows, the other is yellow chevrons which are found on stopways in the pre-threshold area of a runway. These are not load bearing surfaces and may not be used for take off, roll out, etc.

[Beefitarian]

Are the chevrons always yellow? I was thinking about white ones from the get go here. Though after the "X" talk started I started to recall the little regular arrows. <--- also white.