[Peetwo]

Aussie I should have perhaps been more clear, I believe the Slam Dams should have been used on most (if not all) theoretical formulised/calculated splashdown points for MH370, including those not on the 7th arc - why not? After all it is obvious that cost was originally of no objective..

Going back to the BB last on MH370, the discussion continues with more input from Mick in reply to David's... :

David

2 days ago

Mr Bailey repeats his contention that the aircraft descended with fuel for a controlled ditching. Again he does not expound on how this can be compatible with the final satellite communication data, which is consistent with fuel exhaustion.The only possible explanation I have encountered as to how a powered ditching might be consistent likewise  was raised in comments on a 30th January article in the Australian, "Warren Truss concedes....."  I have raised this possibility with the ATSB, which may well have had grounds for dismissing it hitherto. 

What also would need to be addressed under his theory is whether a pilot could plan on the southern Indian Ocean being calm enough for a ditching without aircraft breakup, which would negate its purpose.

A powered ditching would place the aircraft within the search area anyway, though satellite communications with the aircraft at the ditching site would shift the location of the aircraft compared to that at altitude. 

Mick

2 days ago

@David David, the only piece of physical evidence recovered from MH370, the starboard flaperon, does not support Captain Bailey's controlled ditching theory.

Preliminary independent analysis of the damage to the flaperon concludes that "R
epetitive lateral or torsion forces appear most likely at this stage of the analysis. This conclusion, combined with the lack of strong secondary evidence of a trailing edge strike, infers that the disengagement occurred while MH370 was in flight."  

Further independent analysis supports that conclusion and goes on to contend that the flaperon separated from MH370 at altitude and at high speed and that,  "An indication of this comes from: (a)  The ragged trailing edge of the flaperon (with 40 per cent of its total surface area being missing), this being consistent with rapid ‘fluttering’ as would likely occur if the aircraft lost all control surface power whilst travelling at high speed, as would occur when the fuel was exhausted from the two engines ...  and (b) The lugs holding the flaperon to the main wing structure appear to have been torn off in a manner that may be consistent with such violent fluttering (at 10-20 Hz) at high aircraft speed."

Mick

1 day ago

@David David, having just read the Comments from the 30 January article you refer to there are 2 problems with an APU auto-start after a successful controlled ditching:

1.  If the ditching was conducted per training and the ditching check list, the APU switch is turned to OFF, that action closes the both the APU fuel valve and air inlet door.
2.  If the APU was for some reason not set to OFF, after a successful controlled ditching the APU air inlet would almost certainly be at or below the waterline. 

David

1 day ago

@Mick @David Yes the investigators seem to have had good access to the flaperon.  I remain puzzled that there has been no confirmation of these preliminary investigations though and there remains no published outcome of the French investigation. I would like to see a Boeing imprimatur on the general assessment, the manufacturer being aware of flutter and overstress vulnerabilities outside the flight envelope. They might be able to talk to failure sequence. Possibly a lot or research is being done into this.

In the meantime it may be that the ATSB has other reasons to discount the powered ditching possibility. B777 characteristics might well be among them. The APU air inlet beneath the waterline surely would rule it out.

David
1 day ago



@Mick I seem to remember Andrew saying that closing the APU air inlet door was to prevent flooding, reinforcing what you say Mick. Presume this is fuel state independent.

Mick 5ptsFeatured

1 day ago



@David   David, just checking the B777 flight manual and it states:

APU Automatic Start

In flight, if both AC transfer busses lose power, the APU automatically starts, regardless of APU selector position. 

I am pretty sure that the airplane's "in flight" status is determined by the landing gear being retracted and locked or, when the landing gear is lowered, the absence of "weight on wheels".   I seem to recall that the APU auto-start function can be ground tested by jacking the airplane up to take weight off wheels. 

Any old how, it is possible that the APU auto-start might initiate after a successful controlled ditching.   However, the starter will not engage until the APU air inlet door reaches the full open position.  Once the starter has run the APU up to the proper speed, ignition and fuel are provided. When the APU reaches approximately 50 percent, the starter disengages and ignition is turned off.  If the start fails, the APU shuts down automatically and there is no subsequent auto-start. 

Given the location of the APU air inlet, the requirement for the inlet door to reach the fully open position before the starter engages and the delay before fuel and ignition are provided I think the likelihood of the APU actually starting and running long enough to reboot the SDU is extremely remote. 

Mick

1 day ago

@David   I know long shots sometimes get up (Prince of Penzance in last year's Melbourne Cup, for instance) but I think you could pretty well rule a line through an on-water APU start up as the explanation for the seventh handshake.   Contrary to the good Captain's claims of "overwhelming evidence" for a controlled powered ditching, all the real evidence points to an uncontrolled high-speed impact subsequent to fuel exhaustion.   As the Zen Master was fond of saying, "We'll see." 

Andrew

1 day ago

@Mick @David Nope, it wasn't me that said "closing the APU air inlet door was to prevent flooding".
 
The Ditching checklist reads:

"After impact:
FUEL CONTROL switches (both) ..... CUTOFF
APU fire switch ....... Override and pull"

There is no checklist item to select the APU switch OFF before a ditching, and doing so would not prevent an APU auto-start.   The post-impact action of pulling the APU fire switch would certainly kill any autostart attempt, but I doubt that a pilot intent on suicide would bother to complete the checklist.  

Mick is correct in that an APU auto-start is theoretically possible following a ditching, provided the APU fire switch isn't pulled.  That said, the chances of the aircraft ditching intact seem very slim, given the typical sea state in the Southern Indian Ocean.  A broken fuselage would certainly prevent the APU auto-starting, as would an APU inlet full of water!

Mick

@Andrew   Andrew, I'm looking at a Boeing 777 flight manual, albeit not the most current, that has the following check list:

DITCHING
• Send Distress Signal
• Advise Crew and Passengers
• Jettison Fuel As Required
• Accomplish IN RANGE CHECKLIST.
    DEFERRED ITEMS 
==> APPROACH CHECKLIST
- - - - - WHEN BELOW 5000 FEET - - - - -
(OMIT LANDING CHECKLIST)
Ground Proximity Gear Override Switch........................................OVRD
Ground Proximity Terrain Override Switch ...................................OVRD
Pack Switches ..............................................................................OFF
Ensures aircraft is depressurized for opening passenger entry doors.
Outflow Valve Switches................................................................MAN
Outflow Valve Manual Switches................................................. CLOSE
Position outflow valves fully closed.
Prevents water from entering aircraft through the valves.
Seat Belts Selector .........................................................................ON
APU Selector..................................................................................OFF
Closes the fuel valve and air inlet door.

I've skipped over the rest of the Approach check list items, which brings us to:

- - - - - ON THE WATER - - - - -
Fuel Control Switches............................................................ CUTOFF
APU Fire Switch.................................................. OVERRIDE AND PULL
Removes electrical power which ensures passenger entry door flight locks are
unlocked.

Given the importance of ensuring all ingress points for flooding are sealed prior to ditching I'm pretty certain that 
APU Selector..................................................................................OFF
Closes the fuel valve and air inlet door.
should appear on your ditching check list. 

I agree with you, the chance of a successful controlled ditching into the Southern Indian Ocean are slim at best. 


David

22 hours ago

@Mick @Andrew  Andrew, I recall now the remark was about outlet valves, as above, and doubtless not from you.

Can either of you tell me where the APU air inlet is? One informal 777 diag I have shows it top of the fuselage, starboard, just forward of the tail cone. Is that so? I presume it exhausts through the tail cone?

I question whether the pilot would go through either checklist, especially by himself, possibly with subsequent suicide in mind.

Likewise I qualify an earlier post I made about him taking care about sea states. I think he would take his chances as others forced to ditch do. I doubt that authoritative guidance would have been prepared on what sea state is acceptable, for any volunteers, .

The nub of all this though stems from an earlier statement by Mr Bailey that a ditching would entail the aircraft flying further hence his assertion that the search was in the wrong place. This was the important part. Whether or not there was a ditching is of lesser importance to this unsupported assertion, which I believe to be wrong. If the focus of the search was on a ditching, as I see it the locus of the highest probability point for finding the wreckage would shift by a few miles, in my estimate (45deg satellite elevation), five.

Brendan

22 hours ago

Just one point, about the range of flight, it seemed that the distance flown to a controlled ditching with very little remaining fuel would be similar to the distance flown to fuel exhaustion at cruising altitude. But maybe for a long powered glide (which airliners do every day) very little fuel is used in the glide phase.

David

20 hours ago

@Brendan Agree Brendan. Powered descent would need to yield fuel compared to staying at altitude, to fly for two minutes more, have fuel for any loiter to pick ditching direction and have fuel left over. His average speed of advance would be less than that at altitude under power. To me modelling would most likely lead to a spread of solutions, the end point being position and time with some fuel. Fuel consumption needs to be compatible with the estimate, a tolerance being implied.

Andrew

22 hours ago

@David @Mick @Andrew The APU air inlet is located in the top forward right-hand-side of the tail cone.  The exhaust is located in the aft left-hand-side of the tail cone.

David
20 hours ago

@Mick @Andrew If the tail sits high or anyway well above awash and the aircraft remains intact it seems the APU intake and exhaust present no real impediment to the APU running therefore, for a couple of minutes. 

Mick
19 hours ago

@David  Have a look at the pictures from the most successful controlled ditching of a jet airplane in recent times, US Airways Flight 1549.  I know that it's an entirely different type of airplane but after pulling off a text book ditching in still water note how quickly the tail sinks. As I said earlier, I think the likelihood of the APU actually starting and running long enough to reboot the SDU is extremely remote. 

For a controlled powered ditching or powered descent there's still the pesky matter of the seventh handshake.   Under either of those two scenarios the SDU reboot happens when?   Shortly after the airplane has been successfully "soft landed"?   In that case the wreckage should be proximal to the seventh arc. 

Under the ATSB uncontrolled unpowered descent following fuel exhaustion, the wreckage should be within 50 kilometres of the seventh arc. 

Either or, it falls within the current search area. 

David
18 hours ago

@Mick @David Agree Mick that there are various serious impediments opposing the  ditching theory, sea state being one for ditching, APU starting and running and hogging and sagging forces on the fuselage. However my intent here has been directed at the possible, not probable and I would like to know how the 777 floats and in particular what Boeing thinks as to sea states the aircraft might endure in landing and subsequently.
 
I think the unpowered descent could take the aircraft beyond fifty kilometers. But yes in a powered descent it will be close..

Mick
17 hours ago

@David   David, I think I get where you're coming from regarding considering possibilities but the possible should account for the known.  For a controlled ditching to account for the seventh handshake we're assuming APU auto-start after ditching as the cause of the SDU reboot.   That means the airplane was effectively stationary and that is not consistent with the Burst Frequency Offset (the Doppler shift in the transmission frequency) for that transmission (burst).

The BFO for the seventh handshake is anomalous;  it shows that the airplane was moving but not in a manner consistent with the other measured BFOs.   All the other BFOs are consistent with an airplane speed of about Mach 0.84 (560-odd knots) which just happens to be the cruising speed for a B777-200ER.   The last BFO shows a significantly higher airplane speed and because it's point in time it can't be properly correlated as the speed can be in both the horizonta plane (over the ground) and the vertical plane (toward the ground).
 
It is possible that the anomalous BFO for the last handshake was caused by the airplane changing heading, descending and at an increasing speed - what you'd expect from say the start of uncontrolled spiral dive.   It is not possible that the anomalous BFO was generated by an airplane pretty much at rest.

David
16 hours ago

@Mick @David OK Mick I was conscious that the BFO in the last exchange was anomolous and disregarded though the possible connection with a spiral dive is new. And if it rules out a static aircraft that is the end of the ditching possibility.. 

Will take another look at the BFO description and analysis and maybe you could direct me?

Mick
15 hours ago

@David  David,  I can't recall exactly where I read that; it's either in the ATSB Bayesian analysis paper or in one of Michael Exner's papers, probably Comments and Questions re ATSB Report on MH370 released 3 December 2015 or in one of Duncan Steel's papers, possibly Background Information on the Pinging of MH370 by Inmarsat-3F1. 

When I get a chance I'll go back over the various papers and see if I can pinpoint it. 
I hasten to add that "It is possible that the anomalous BFO for the last handshake was caused by the airplane changing heading, descending and at an increasing speed" is my interpretation not one I've read elsewhere. 


David
1 hour ago

@Mick Hello Mick. In the Definition of Search Area and Bayesian Methods Reports I cannot find any statement that the last handshake's BFO "shows a significantly higher airplane speed". Nor can I find where an aircraft being stationary "is not consistent with the BFO."  

What I can find is what I have earlier understood to be the case. The Bayesian Report (p7) says that the BFOs at the time in question (and one other) are "deemed unreliable at these times and cannot be used." The cause is that the messages concerned "occurred during transient phases of SATCOM equipment so cannot be used".

That Report (p26) describes how aircraft software compensates for Doppler shift, the residual Doppler data stemming from the aircraft assuming that the satellite is fixed relative to earth, which it isn't.
 
However the Report does add that the aircraft does not compensate for any vertical component of aircraft velocity. So if you reject the above explanation as to why these BFO data cannot be used, you could conjecture a spiral descent might be the source of corruption, though that would account for just one of the two BFO anomalies. Even if you did this would not cover why a stationary aircraft would cause a problem.. 

Maybe I have missed something in which case I hope you will put me right; but if not I do not agree that the final BFO rules out a powered ditching leading to a stationary aircraft. Quite probably something does, but as currently it stands, not that.

MTF...P2