Landing Distance Discussion

[AKAAB]

Let's take the discussion of landing distances into another thread and keep from speculating on the "facts" involving SWA's runway excursion. Some legitimate questions have been raised that may provide insight to others learning our craft.

Fair enough, this is all I will post. I still wonder though, how when our 15,000 lb airplane with a 95 knot ref can't meet a 135 landing there, how can a 737? Sorry to bother you.

To answer a legitimate question - it all depends on how your aircraft was designed and certified. I'd be willing to bet that your 15,000lb/95knot ref airplane has pretty small wheels and brakes. (What model was it?) Every corporate jet I flew in my previous life did not consider the use of reverse thrust in determining landing distances. In fact, when a new aircraft model is delivered to the first customer it often does not have operable reversers - like the Lear45 if I recall correctly. The reverser certification comes after the certification of the airframe. That's not the case on transport category aircraft. On the Airbus, reverse thrust is considered in the calculation of required runway distance.

Is that the case on the 737? Can someone tell us if the 737 considers reverse thrust in landing calculations?

Also, like your aircraft, there isn't a corporate jet I've flown, with the exception of the CE500, that wouldn't have benefitted from bigger brakes. But, bigger brakes means more weight and higher overhaul/operating costs. The designers have to make the aircraft safe and maximize performance - i.e. keep the weight down. The Lear60 was first delivered with the same brakes that the lighter Lear55 had because it was a system that was already certified. In my opinion, it needed bigger brakes - don't know if they ever made the upgrade we were promised many years ago.

Would any of you erudite pilots like to open the discussion of brake energy?

 

[Viffer]

Good post, and the airplane I mentioned is a 500 series Citation. The advisory information for contamination takes the takeoff and landing distances WAY over 6500 feet at even light weights. I have flown a few airplanes in your profile as well, and none of them could make that either if the contamination was taken into account. For my own knowledge, how does boeing present contaminated runway correction factors to the pilots? And are 121 ops bound to any similar rules as 135 such as the 60%/80% of available landing distance, and the 15% penalties for non dry and low vis?

 

[ATRedneck]

And are 121 ops bound to any similar rules as 135 such as the 60%/80% of available landing distance, and the 15% penalties for non dry and low vis?

***deleted***

I had an entirely too-long answer about takeoff performance, not at all relevant to this discussion.

Carry on.

 

[MJG]

Something else to consider. How many of you have started down the approach with reports from the tower and other aircraft of ok braking action, no windshear etc. only to find out for yourself firsthand that it was much worse than you thought/realized. I've found that the ba reports and runway condition reports can be deceiving at best. There are some factors out there that are beyond your control. Especially when you combine strong winds with slick runways. The books may say you're ok to land but that doesn't mean it's going to turn out that way. Let's all be careful this winter.

 

[HawkerF/O]

The aircraft size and weight has nothing to do with the landing #s. Its size signature is not proportinate with landings #s. A Global Express is what, close to 100K puonds? It has a huge wing and a big 'ol fat slat and has ref speeds (30% above a stall) in the high 90s and low 100s. Falcon 50 same thing: 35K pounds, slat, efficient wing, 1 T/R and nice brakes. Those aircraft cound do 4 or 5K foot strips all day long 135 and they weigh much more than the 15,000LB 95 knot ref airplane.

 

[Viffer]

So the runway/airport analysis charts give the maximum weights, given conditions. I assume for landings it is the same system? If you don't mind how many levels of contamination do those charts give the pilot? Every contamination chart I have used has many levels of wet, different catagories of snow for different depths and compactedness. This is what I am finding suprising, if it is true, that detailed contamination is not easily or readily accessable to the crew, and what would happen to the crew who refused a landing, or takeoff, even if the analysis chart conditions were met? By this I mean if the chart just says loose snow for instance, but the runway has compacted snow from the plows under new loose snow, do you have the means to take that into account? And I appreciate your help learning about this. I am being asked a lot by non aviation friends and family about 121 ops, and I don't want to speak without knowing something about it.

 

[Viffer]

The aircraft size and weight has nothing to do with the landing #s. Its size signature is not proportinate with landings #s. A Global Express is what, close to 100K puonds? It has a huge wing and a big 'ol fat slat and has ref speeds (30% above a stall) in the high 90s and low 100s. Falcon 50 same thing: 35K pounds, slat, efficient wing, 1 T/R and nice brakes. Those aircraft cound do 4 or 5K foot strips all day long 135 and they weigh much more than the 15,000LB 95 knot ref airplane.

Of course every plane is different, but put an inch of snow down and 135 an airplane would need to be able to stop in 4000 , with at least 15% added to it's book distanc plus a cumulative 15% on top of that if the vis is down. Can the Global do this taking contamination into account? Can a Boeing? This little 500 Citation can't even do that and it can stop shorter than just about anything. Neither could some four engine jets I used to fly with reversers as big as a drag shoot. All I am saying, or asking, is to what extent are crews, myself included, taking contamination into consideration for winter ops. Wet numbers are irrelevent for a snow covered runway, and I am sure that there is at least advisory information available for all airplanes for these conditions.

 

[vtc12ip]

Something else to consider with regard to braking action. The first 2/3's of a runway is where most of the traffic is. Hence braking action reports are representative of that portion of the runway. Once past the 2/3's point, the braking action generally decreases. Sometimes by as much as two catagories. Most people are surprised by the amount of runway needed to slow when the braking action is over reported.

TWR: "XYZ 123 how's the braking action"

XYZ 123: "Ah, we'll call it really poor"

Better to be surprised on a runway with plenty of room to accomodate your surprise.

 

[OleGuy]

In my previous life Boeing performance numbers never included reverse thrust. The runway landings numbers were either wet or dry, no scale. Only restriction being no landing authorized with nil braking report or more than 4" of snow on the runway. One of the old guys I started with would always ask whomever gave him a nil braking report how the crew was, since they had to have run off the end...... Auto brakes were not required by ops specs. The one thing that I always appreciated in 121 was that a go/no go safety decesion was never forced on a captain. There are so many variables that go into decesions that I, unlike some, don't believe everything can be included in a flow chart. Common sense must guide you, how experienced are you in this situation, experience of the rest of the crew, which end of the performance envelope, and many more factors weigh in on the prudent decesions.

 

[Wesb737fo]

Hey Dudes,

I have flown the 737 into MDW during winter ops. You can make the numbers work most of the time. I'm waiting until the facts come out, but it will be interesting to see where they touched down, how fast they were going, and the actual wind conditions. There are specific criteria for WSR operations. I'll reserve judgement until I see the data, however, it is a good discussion.

ldg distance for runways with good medium, and poor reported braking action are 115% of actual ldg distances and do not include the 1.67 regulatory factor reverse thrust. It is not used to determine dispatch required landing field length.

BTW, I drove through that intersection (55th and Central) a few hours before and I couldn't get good traction. The weather came in and conditions deteriorated rather quickly.

"OleGuy" said it best. You sir are a very wise man.

 

[AKAAB]

Regarding Viffer's question on how we consider contamination - although we have performance charts for backup, we use a computer to that calculates our required distances. Various types and levels of contamination are taken into consideration - i.e. dry snow, wet snow, slush, wet, etc. - as well as status of required systems like reversers, ground spoilers and brakes. The computer displays landing distances with normal, low and medium autobrakes and indicates if the distance is predicated on the basic runway length or the distance beyond the glideslope ( an important distinction if you are an MD-11 landing in EWR).

 

[millhouse21]

NTSB just said winds were 090-13. They were landing on 31 right?

 

[AKAAB]

NTSB just said winds were 090-13. They were landing on 31 right?

It might be better if you post this question to the SWA thread instead of here. We are having a discussion on landing distance calculations here and are trying to avoid speculation on the SWA-MDW accident. The other thread is the right place to add specific questions about SWA at MDW.

Cheers!

AKAAB

 

[MNR]

The Lear 60 did get an upgrade to the brakes that just recently became avaiable. It adds an extra set of pads. It however does not change the landing numbers. Rumor is that if the Air Force buys a bunch they will be redoing the landing distances. Any discussion involveing 135 landing distances should include ther Lear 60. Those breaks are the same ones they used on the 23.

I fly a 60 out of MDW and there have been times where we had to be very careful about planning for weight and landing distances on arrival. The 60 is one of the more piggish corporate aircraft when it comes to runway distances. Ref speeds are commonly around 130ish and I like to have 6000ft dry. Distances average around the 3300ft mark so its close. That being said even before part 135.4 was published and put into effect we could get into MDW even when it was wet, if we kept our weight down. The reversers are not taken into account for landing distances. They work really well. So 99% of the time I am comfortable with it the numbers fit in the 60% or 80%

Part 135.4 allows you to be classified as an "eligable on-demand" operator. In which case you can use 80% of a runway in your calculations instead of 60%. This is if you meet the conditions in Part 135.385(f).

Break energy is another consideration we have to make regularly. Its limitations center around takeoff within 30 minutes of landings over certain weights and attempts to takeoff after aborts.

Ultimately, its not just a function of weight and ref speed but of op specs, wing shape, wing supplimental lift surfaces, regulations, etc.. My guess is the numbers were there to make the landing attampt.

 

[ualdriver]

I'll throw my 2 cents in. I think this thread is an excellent thread for us professionals to think about when landing in these kind of conditions. I'm a 737 Captain and I have my book in front of me for the 737-300/500 aircraft, although I'll use the -300 numbers since it is the heavier aircraft. I'm referring to the 737-300 demonstrated landing distance charts (flaps 40, which is the flap setting one would use with a short runway/questionable braking action) and some notes in the landing section of the chapter at our airline.

First of all, the demonstrated landing distance is based upon the minimum landing distance demonstrated during certification (i.e. Boeing's equiavalent of Chuck Yeager at the controls) with maximum braking, crossing the threshold at 50' at the appropriate REF speed. No reverse is used (although our charts include it) but spoilers are used.

Here are the notes at the top of the chart:

-Ref at threshold
-threshold crossing height 50'
-touchdown 1000' past threshold
-1% downhill slope
-Max manual braking with max reverse OR MAX autobrake setting with no reverse

Adjustments:
subtract 15 feet per knot of HW
add 50 feet per knot above REF speed
add 150 feet per knot of tailwind
add 500 feet for use of manual speed brakes ( I don't think SWA has autobrakes so this comes into play)

So assuming that the pilot flying was just as capable as a Boeing test pilot and the aircraft was functioning perfectly, here are some landing distances to chew on. Keep in mind that these distances include the 1000' of runway behind the pilot when he touches down per the note on the chart. Landing weights of around 100,00-110,000 lbs are common for our 737-300's.

Sea Level, GOOD braking action, landing weights below:
80,000lbs. 2,925 ft.
100,000lbs. 3,385 ft.
120,000 lbs. 4,175 ft.
130,000 lbs. 4,625 ft. (max take-off weght)

Sea Level, Braking action Fair/Medium, landing weights below:

80,000 lbs: 3,810 ft.
100,000 lbs: 4,490 ft.
120,000 lbs: 5,373 ft.
130,000 lbs: 5,748 ft. (max take-off weight)

Sea Level, braking action poor, landing weights below:

80,000 lbs: 4,880 ft.
100,000 lbs: 5,800 ft.
120,000 lbs: 6,848 ft.
130,000 lbs: 7,393 ft.

You can see that even with braking action as FAIR, at typical landing weights, touching down 2000' down the runway at MDW suddenly becomes a very big deal. Not going immediately to max reverse and max braking in these conditions at MDW suddenly becomes a very big deal. Just a few knots of tailwind at MDW become a very big deal. Something for us to all think about when we operate on contaminated runways on those dark and stormy nights.

But for the grace of God go I.

 

[Bjetset2]

Runway Performance

Good post, and the airplane I mentioned is a 500 series Citation. The advisory information for contamination takes the takeoff and landing distances WAY over 6500 feet at even light weights. I have flown a few airplanes in your profile as well, and none of them could make that either if the contamination was taken into account. For my own knowledge, how does boeing present contaminated runway correction factors to the pilots? And are 121 ops bound to any similar rules as 135 such as the 60%/80% of available landing distance, and the 15% penalties for non dry and low vis?

Anit-Skid makes a HUGE difference in runway numbers. Does your CE500 have TRUE anti-skid or just the "toe vibrators" for the brake pedals that mine had? This might be the difference. Food for thought

 

[Groucho]

NTSB / FAA findings

Landing / Stopping distances represent another area where the published data may or may not provide enough information to allow an operator to operate safetly.

I am sure that the Fed's will look at all the calculations and the reported conditions to determine if it even could be determined that a safe landing could be made. The tapes will show all the flight parameters and there may or may not be measureable braking action data.

The end result of this may be a push toward more stringent landing / runway contamination requirements.

The last set of accidents involving takeoffs in icing conditions resulted in improved deicing procedures. Contaminated runway landing distances may now recieve greater scrutiny even though the fatality count to these accidents is low.

Just my $.02

 

[B6Guy]

C 500 stopping

The main reason that the Citation has pretty poor contaminated-runway numbers is because the wing does not have big spoilers. The C 500 has two small 'airbrakes' one above and one under the wing, and they have almost no effect on lift, only on drag.

Every 121 aircraft that I'm aware of have very large spoilers covering most of the wing span. Upon landing the auto-spoilers deploy with either wheel spin-up or squat switches or both.

With the deployment of the wing spoilers, a majority of the weight of the aircraft is then on the tires, there is very little residual lift from the wing. The tires then have lots of weight per square inch of contact area which provides much more friction on contaminated surfaces.

It is very hard to compare the Citation landing distances to any aircraft with large lift-dumping spoilers.

Another issue is the tailwind component, The tower wind and the atis reported wind is at a given height AGL. Around 50' AGL usually. But very often the actual tailwind at 100-200' is several times higher. A heavy 121 aircraft won't slow down and be right at Vref when the tailwind drops from say 25 kts to 5 kts in the last 100' on final.

B6Guy

 

[73-Driver]

Another issue is the tailwind component, The tower wind and the atis reported wind is at a given height AGL. Around 50' AGL usually. But very often the actual tailwind at 100-200' is several times higher. A heavy 121 aircraft won't slow down and be right at Vref when the tailwind drops from say 25 kts to 5 kts in the last 100' on final.

B6Guy

Speaking from experience, how many times have you been on final to 31C with winds reported lighter than what has been calculated by the FMC.

 

[B6Guy]

Exactly??

Since I don't fly into MDW anymore, I can't remember specifics to 31C. But in general, and that is what we are talking about, not the specific WX at MDW, the winds are very often a lot higher at a few hundred feet than they are at 50' and what are reported by atis.

Example: we fly into LGB where the wind is often reported as 180/09. Landing on rwy 30. At 200' I've seen 170/20 many times. At 100' they are down to very close as advertised. This is just an example, your results may vary. There is nothing illegal here, performance calculations are based on reported winds, but the realilty can often be less than optimal.

B6Guy