Old myths?

[Uptrim Disable]

Every now and then I fly with captains who consistently go well into the "too-much-red" area on the PAPI or PLASI. This way, they claim, they'll greatly reduce the landing distance.
I cannot really understand why? One thing is that a downdraught might send us straight into the LLZ antenna / ground, but doesn't a shallow approach angle always give a longer landing distance?
Helicopters have the shortest LD and they have an AA of 80-90 degrees ;-)

Others insist that we "get on the step" when leveling off at a "high" cruising altitude (climbing to 25.300' and then diving back to 25.000' to accelerate faster! Why would one want to gain extra potential energy, just to trade it off for kinetic energy thirty seconds later? Why not start the acceleration earlier and at the same time avoid a level bust? (I can't believe that today's turboprops are that underpowered that the power available curve tangents the power required curve at 25.000', thus justifying "the step"..?)

Well?

[oxford blue]

On the landing distance question, I don't think that the theory is that a flatter slope is a good thing in itself if you land at the same touch-down point. The idea is that by being low, you will land right at the start of the runway (on the piano keys, as the RAF used to say) instead of a third of the way down it. That will reduce your total landing distance.

On the seond question, I, too, have flown with pilots who do it. I think it's very hard to justify in logic (though some other contributor may be able to do it), but intuitively, it does 'feel' as though it works. On an underpowered aircraft at altitude, you do seem to hit the target speed quicker.

[Hew Jampton]

The PAPIS 'correct' angle is there for a purpose and that's to indicate an approach path that gives internationally-agreed safe obstacle clearance. Yes, a shallower approach angle can give an earlier touchdown and shorter landing distance but it also increases the risk of hitting an obstacle or touching down in the undershoot area, both of which can shorten careers rather than landing distances, to say nothing of the consequences of the 'accident' itself. If you have access to a confidential reporting system like UK CHIRP or an equivalent in-house scheme, use it. It is an unfortunate fact of life that if your captain screws up and it is shown that you sat there and did nothing, especially if you knew that it had been happening "consistently", some of the fertilizer that hits the air conditioning will come your way.

On 'the step', doubtless the aerodynamics experts will comment but I think it only applies if flying near the very bottom of the drag curve, ie at max endurance speed. If the bottom of the curve is a U shape, with the very bottom being max endurance, there will be two speeds for a given power setting just above max endurance power. One of these will be 'on the back of the drag curve', ie inefficient and the other will be on the correct, efficient, side, probably at or near max range speed. 'Getting on the step' involves a belief that this practice ensures the aircraft is on the right side of the drag curve. However, especially with the advent of TCAS and level-bust monitoring both from flight recorder and radar data, I think it is wrong deliberately to bust a level, even temporarily. If it becomes part of a company's or an individual's unofficial SOP to bust the level by, say, 300 feet and the Pilot Not Flying routinely ignores it because "It's just to get on the step", one day it will be a proper level bust, ie complete failure to level off and it will have been ignored by PNF, even if PF has pre-announced his/her 'step' intentions. Again, you might consider submitting a confidential flight safety report.

[Slasher]

Yeh that first question relates to another thread I started about one-dot low approaches. Dont know about this 3 or 4 reds business!

WRT putting the aircraft 'on the step' Uptrim, which particular aircraft are you referring to specificaly?

[Capt Pit Bull]

I wouldn't sweat being slightly off the PAPIs.

Why?

Plenty of places they don't agree with the ILS G/S that well anyway.

Plenty of other places don't have them full stop, and presumably you wouldn't refuse a visual approach.

CPB

[Uptrim Disable]

Slasher: It's the DHC-8-100...

[OzExpat]

Hmmm, yeah, lower approach angle, less wheel clearance before the runway - more chance to hit something that could really spoil your day. There is a potential for tailstrike on landing, in longer bodied aircraft too. I've made much the same points on the thread that Slash started.

I tend to agree with CPB about being slightly low on a PAPI or VASIS but it's a "horses for courses" issue. I certainly don't have a problem with that in the Kingair. But, as Slash has said, a deliberate deviation well into the reds is a real worry, IMHO.

As for "the step"... I've been flying Kingairs since 1986 and have never seen the necessity to bust the cruise altitude to dive back down to it. I find that the aeroplane only needs a couple of minutes to accelerate after levelling off from the climb. Then set cruise RPM (1700 RPM) and sit there fat, dumb and happy.

Why complicate something that doesn't need complicating?

I guess there's one further point that I should make here about PAPI/VASIS approach angles. Part of my job entails periodic flight checks of the various approach path angles.

It can be very difficult to maintain any particular approach angle in turbulent flying conditions. One of the checks involves a deep penetration into the reds, to check terrain clearance and I can assure you that, once you're seeing 3-4 reds on a PAPI, or mostly red on a VASIS, you have no real idea of the actual angle of the approach. You are also vulnerable to further excursion downward due to turbulence.

I've been doing the same job for 16 years so I've got a few ideas on how to do it safely. But, all things considered, this is not the sort of thing that a professional airline pilot should be attempting, even in a flexible aeroplane like a Dash-8.

[m&v]

At one time ,as we all know,all the g/slopes were 2.5(ICAO).Then over the last few decades 3degrees is the accepted stndrd.As has been pointed out low on the Vasi puts one on the end -to use the longer runway dis available.(3 degrees touches one down about a 1000' into the runway dis.)..2.5 touchdon closer to the end ,but faster ergo one uses the extra dis.
(a 90 degree g/slope provides the least rollout)
Getting on the step stems from the 'heavy metal' days of the piston era,trim it level???and get the 'cruise' speed up...Even the DC8 needed some tlc on initial cruise..
In Canada the policy is to only establish Vasi/papi on Non precision approaches(some have with the ILS),but they very rarely align themselves-there just provide slope guidance once Visual.
Cheers..(is it my round??):confused:

[Uptrim Disable]

As additional info, we frequently fly PLASIs set at 4.5deg or more, and have a CAA approval of using 35' as ref. height at threshold...

[Human Factor]

If you're in something smallish, landing on the piano keys won't be a problem. As the maxim goes: runway behind is like sky above ....

There are certain circumstances where it is clearly beneficial to use every inch of runway (just ask the US Navy!!) although when you're in the big jets, if you plan to land on the piano keys, you'll drag the tail through the approach lights!:eek:

[Wino]

HUMAN FACTORS,

Just remember, you LAND LONG and CRASH SHORT.
Even the USnavy tries for the middle of the deck (3 wire...) not the wire right near the fantail...

Cheers
Wino

[error_401]

Also consider this!

When flying either 4 white or red you're out of - let's say scale.

Wo when flying 4 reds on a PAPI who tells you that you are not already on a 1.5 deg glide slope?

I'd never fly a PAPI that way. Max allowance is 3 red 1 white
;)

Or - disregard it tell your PNF and fly a visual approach aiming point. That is what we have been thought.

[Captain Stable]

HF there is another matter, which is the published performance figures.

These assume a correctly-flown approach - i.e. on glideslope and hit in the TDZ. If you do that, and the figures say you can stop in the distance available, then you can (and the editor's decision is final :D ).

If you come in at a shallower angle, but with the same speed, then it is because you have more engine power on than for a correctly-configured approach. With a lower rate of descent, same speed and more engine power you actually have a higher-energy approach. As you come into ground effect that will give you a bit more oomph than you really need. Big engines take longer to spool down. You don't want that!