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Pax Jet in water at NAS Jacksonville, all OK

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Pax Jet in water at NAS Jacksonville, all OK

Old 24th May 2019, 11:45
  #101 (permalink)  
 
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Originally Posted by FlightDetent

The lateral deviations around the centerline are pronounced, I think there might be more to it than just a simple handling deviation. We'll learn eventually.
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I think this post from earlier in the thread provides pretty good insight into why the aircraft wound up in the river - particularly the part about the speed at touchdown.

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Originally Posted by 737 Driver
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In the NTSB briefing (link posted above) it was stated that the available landing distance for this runway was 7800 feet. At maximum landing weight on a wet grooved runway, a 737NG will require approximately 6800 feet of runway with both reversers, Flaps 30, max braking (air distance included). On a wet ungrooved runway (braking advisory medium), the calculated landing distance exceeds 8,300 feet. If braking action was medium to poor, the calculated distance exceeds 9500 feet. To be fair, all of these calculations are conservative, and demonstrated performance is usually better. The landing data calculator I have only gives a choice of both reversers or no reversers, again conservative for the one reverser inop scenario. Those calculations start at 8300 feet for the best case braking conditions and exceed 12,000 for medium/poor braking.

I do not know the actual landing weight, however according to the preliminary data the incident aircraft touched down at approximately 15 knots faster than the maximum weight Flaps 30 approach speed with a 15 knot tailwind. This is 30 knots total faster than the entry condition for the calculations above. Given what we currently know, it does not appear that the aircraft could have been stopped within the confines of the runway even if they had landed in the touchdown zone with no subsequent bounce.
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Old 25th May 2019, 16:16
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Preliminary report is out, but I can't post the link.
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Old 25th May 2019, 22:18
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https://www.ntsb.gov/investigations/...ive-update.pdf

just an update afaict
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Old 26th May 2019, 07:03
  #104 (permalink)  

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@yoko1 the NTSB leaflet still does not have any speed information, so waiting for an authoritative source.

The numbers in 737 driver's post are inconclusive. Most likely they explain the flight couldn't had dispatched towards that particular runway, not why it did not stop (planning margins are +66%). I queried that already here.
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Old 26th May 2019, 07:15
  #105 (permalink)  

Only half a speed-brake
 
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FIRESYSOK
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Old 28th May 2019, 17:29
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NTSB Investigative Update - 5/23/2019


https://www.ntsb.gov/investigations/...ive-update.pdf
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Old 28th May 2019, 18:04
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Do we think the plane would have stopped in time had it remained on the paved runoff area instead of taking the excursion through the grass?
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Old 30th May 2019, 09:11
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FO had 19 hours on B737 and was on an operational experience flight. Makes me wonder if he could feel bold enough to challenge the Captain to continue on in such marginal conditions..

G
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Old 30th May 2019, 09:57
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FO Experience.

Now that is interesting, we call it line-training and has to be done by a dedicated errr, Line Trainer.
This comes with certain restrictions, in this case a safety pilot ( First few days, some 8 to 12 sectors I think)
Now I know the entry level is different in FAA world, BUT I think we are looking at a rather interesting case here.
Considering the resent discussions with regards to the Max and crew training etc.

Just for the record , this scenario is the ultimate 737-800 killer.
Get this one wrong , and You WILL go offroading!
Lucky they were!
To be continued...

Cpt B
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Old 30th May 2019, 13:32
  #110 (permalink)  

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Captain B, given your experience

If somebody presented this landing possibility to you, with
- given LDA
- wet surface, reported Good BA
- 10 kt tailwind,

Could you run the numbers and tell us how much margin comes out of it? Assuming wildly 150 male pax at 85 kg each, 300 bags x 25 each, and 4 tonnes of fuel upon landing.
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Old 30th May 2019, 14:48
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Flight Detent

Indeed I did.
Just cracked a Cuban after some iPad number juggeling.

First it was mission impossible as Your 150 men and 300 bags and 4000kg landing fuel put me over Max Landing wt 65385kr
No bother , I chucked some luggage and decided 64 ton was plenty.
Next , dont have this airport so I used Stavanger ENZV rwy 36.
Flat as a pancake,TORA 2556m/8385f more importantly LDA 2406m / 7894f . So basically as rwy 10 at 9000feet minus 1000 displaced threshold.
Conditions:
Wet Ba Good
10 tail
22c
Q 1013
Flap 30
1 Rev Inop
Vref30+5 : 151kts
Autobrake Max 2167m
Max manual brake 2028m
( Atutobrake 3 gives 2511m , to long!!)

Sooooo.
In Theory doable.

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Old 30th May 2019, 14:59
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That being said:
Any change in this performance and OFF You go.
So BA good goes to Medium / good and 2483m with autobrake Max and Voila, You have crossed the 4 lane Highway to Stavanger.
( Max manual brake could save the daywith 2386m leaving You 8 meter to spare!!)

Any faster speed , floating , gust, auaplaning or delay of the single reverse is offcource pushing You further out into the Bay, faster.

Not the first time in an 800
Not the last.
To be continued.,,,
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Old 30th May 2019, 20:00
  #113 (permalink)  
 
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Wet figures always need to be filtered through the lens of FAA SAFO 15009 Turbojet Braking Performance on Wet Runways
Subject: Turbojet Braking Performance on Wet Runways

Purpose: This SAFO warns airplane operators and pilots that the advisory data for wet runway landings may not provide a safe stopping margin under all conditions.

Background: Landing overruns which occur on wet runways typically involve multiple contributing factors such as long touchdown, improper use of deceleration devices, tailwind and less available friction than expected. Several recent runway landing incidents/accidents have raised concerns with wet runway stopping performance assumptions. Analysis of the stopping data from these incidents/accidents indicates the braking coefficient of friction in each case was significantly lower than expected for a wet runway as defined by the Federal Aviation Administration (FAA) in Federal Air Regulation (FAR) 25.109 and Advisory Circular (AC) 25-7C methods. These incidents/accidents occurred on both grooved and ungrooved or non-Porous Friction Course overlay (PFC) runways. The data indicates that applying a 15% safety margin to wet runway time-of-arrival advisory data as, recommended by SAFO 06012, may be inadequate in certain wet runway conditions

For non-grooved or non-PFC runways, experience has shown that wheel braking may be degraded when the runway is very wet. If active moderate or heavy precipitation exists, the operator should consider additional conservatism in their time-of-arrival assessment. For grooved or PFC runways, experience has shown that wheel braking is degraded when the runway is very wet. If active heavy precipitation exists; the operator should consider additional conservatism in their time-of-arrival assessment..
If I recall from the initial report the rainfall in the last hour prior to landing was 16mm, in the heavy region for rainfall intensity. Boeing talk about not landing in very heavy rainfall, but given that heavy starts at >7.6mm per hour and violent at >50mm per hour there is a large ambiguity for the heavy to be located in this range. Reports passed to the crew consistently mentioned heavy rain and thunderstorms at and around the field.

Given SAFO 15009 and the conditions is surprising the aircraft failed to stop on the runway?

Here is another 737-800 near over-run investigation that looks at the issue of reduced wet braking effectiveness in more depth : Reduced braking effectiveness during landing involving Boeing 737-800, VH-VOP at Christchurch Airport, New Zealand on 11 May 2015 (full pdf report available on that page)
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Old 31st May 2019, 09:30
  #114 (permalink)  

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Curtain, is that the report which avoids describing the touchdown point and speed?

Well, ff that's what it takes to point out that present-day performance criteria do not allow for degradation of friction towards the far end, we should still be boldly thankful.

My personal irk is frozen ruts or wet compacted snow at the DER line-up position, but the rubber deposits at the far TDZ when wet probably present even a larger problem.


Capt. B, and when you have a moment:...

For the second run, let's call it 170 servicemen @85 kg with 1x 23 kgs bag each = payload 18.360 kg, and add 3,640 landing fuel ==>> LW = DOW + 22000 t ( I hope the -800 can do).

Since you have an electronic tool, the figures you gave us, are those:
- result for dispatch calculation, RLD?
- AFM/FCOM perf data ALD?
- operational figures F-LD = ALD + 15%?

because

For -800's direct competitor, payload and fuel as per above: results in LW = MLW - 1000 kg.
RLD = 2940 m
FLD = 2254 m
ALD = 1960 m
DLD = 1822 m

There several dots I am trying to connect. For my future landings, as well as for those who might imitate what they see me do. In a systematic manner, where the difference between the assumed and actual performance of weight, aerodynamics, braking friction, and human factors too will be accounted for - when the time is due. Not before the hard facts are established and verified. Thus at this stage, for illustration and using my aircraft's data, with LDA of 9000 ft = 2743 m

Dot One: Would I be legal to dispatch?
No, not into 10 kt TW scenario. But we would pick the more favourable runway during the calculation and be legal to go.
- 2310 RLD for zero TW = legal to go
- 2650 RDL for 5 kt TW = legal to go
Yes, we actually would.

Dot Two: Would I be legal to start the approach?
Yes.
- 2254 FLD

Dot Three: Overrun awareness. How much of a perceived margin would I have in mind before the attempted landing?
Not really critical, rarely any alarm at all.
- 783 m margin. LD-ALD.

there are more dots, of course.

Dot Last minus one: Which of the above calculations is going to fail me?

The ultimate dot: How do I notice in case fan suck the sheets?

Over to you...
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Old 31st May 2019, 10:36
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FD
I like Your project, but I have a rather tight agenda today.
That said , I must say that most of these things are paper exercises, err iPad exercises.
I have a few times gone sliding in Turbo Props , no big deal.
Once in the 737-800, never again.
What was my problem?
Rime and deicefluid on rwy, BA good!
43 min earlier.
F40 , full reverse, autobrake 3. nice decell.
60 kts - idle reverse: NADA, POOR BA, sideways slide all 62 tons worth.
Auto brake off, Centreline , Full reverse, Gentle brake.
Warned the chap at 8 nm final.
He lands
RWY closed after a few harsh words.

Point: Only ONE of many factors has to go south , and off You go.
To be continued
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Old 31st May 2019, 12:02
  #116 (permalink)  
 
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I have always been bemused by the 15% rule. For decades here, it was 1.67 x the ALD ("demonstrated Landing Distance"), before and during flight.

Then a few years ago our regs changed to the inflight requirement being 1.15 x ALD. That's pretty tight even when everything goes right.

What's the point of having different rules when the wheels are in the well?
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Old 31st May 2019, 12:11
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Read somewhere (can't find it) that the runway was not grooved which makes a pretty big difference in the landing distance when there is substantial water on the runway.
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Old 31st May 2019, 15:33
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When you're on the ground, if the numbers don't work, you have the option of just not taking off. Once "the wheels are in the well" you may need less stringent rules if things go pear-shaped and you have to land in a tight spot.

Consider Qantas 32 - they didn't even make 1.15 x ALD. (I think it was more like 1.03 calculated, and in the event, actual). But it was "try or die."
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Old 1st Jun 2019, 01:00
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I appreciate that; I just don't understand the logic allowing us to reduce to 15% for a normal landing just because we are now airborne.
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Old 1st Jun 2019, 02:31
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If I'm reading between the lines, the logic is because the dispatcher could use the most favourable forecast best case environment conditions at the planned arrival time to maximise payload. Airborne at your destination, those conditions may not actually exist. The only alternative is to divert if that possibility exist.

The reduced enroute factoring appear to be a commercial fudge to allow you to get to your destination. The bigger question is, should you?
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