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Author Topic: The flight plan, magnetic course, headwinds.  (Read 384716 times)

Erik

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Re: The flight plan, magnetic course, headwinds.
« Reply #60 on: January 02, 2012, 07:20:18 PM »



Pilots are trained to check their DG about every 10 minutes so Earhart would have caught the errors you are concerned about after only a short period of time.
We dont know for sure.  What if she forgot to check for 2-3 times in a row?  Or what if she had checked and made a simple interpretation mistake?  This is where experimenting with possible scenarios, helps us come up with ideas that generate other ideas to help solve this riddle.
Firstoff, it's hard to misinterpret. Secondly, a precessing DG doesn't affect Noonan's compass. (They did find a note floating on the sea not far from Howland (the Coast Guard covered this up) that said "Amela, get back on course, my compass shows you way off!" ;)



Quote
Real precession is normally very small (unless the DG has been damaged or the bearings are very worn.) 
This is exactly what I was suggesting.  I wasn't very clear in my original post, but I meant that the 'real' precession was being affected by this phenomenon of mechanical failure.  What if the DG was experiencing a slight wear, or if a vacum leak was gradually getting worse?  Imagine they didn't catch this fact for 30-45min, and found themeselves gradually flying 5-10 degrees off course.  When they caught the error (assuming no celestial observations), how would they have been able to get back on the original course line?

RESPONSE
--------------------------------------------
The DG was a new instrument that had very few hours on it so the bearings should not have been worn. Also, the autopilot had it's own gyro that was independent of the pilot's DG so it is unlikely that they would both precess exactly the same amount, any discrepancy between the two would have been quickly noticed by Earhart.

gl

"New" doesn't always equate to working correctly.  Unless your a manufacturer of course - then everything works perfectly! Right Gary?  ;)  I'm sure Ric would be happy to point out situations where he has seen brand new equipment fail.  Instead of wear, let's say for grins that there was slight mechanical defect or vacum leak affecting the gyros?

Either way, both systems were operating on the same vacum - correct?  What about a vacum "issue".  Even if not, and the autopilot was a "wing-leveler" only, then it wouldn't matter much.  It would essentially mean AE was flying by hand adjusting the "wing-leveler" to match DG.

Does anyone happen to have any details on the Electra's pitot/static configuration?  Vacum configuration?  Or more details on Noonan's compass?
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Erik

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Re: The flight plan, magnetic course, headwinds.
« Reply #61 on: January 02, 2012, 07:33:50 PM »

in looking at the recent posts in this thread one thing leaps to the forefront.  There "was" an error.  When was the "error" detected?  When the error was detected would dictate your corrective action, would it not?  A gradual return to course if discovered early on, or a dramatic change in course if discovered later on.  There were no indications from radio signals of "any" navigation issues being detected.  In fact the radio message"We must be on you..." suggests that at least AE thought she knew where she was.  Other radio messages give positions like "200 miles out".  A sign that they know where they are. 
That throughout the flight AE was making radio calls reporting "everything is OK" indicates that they thought they knew where they were.  Its also my main objection to the Long theory that they opened up the throttles and arrived at Howland with minimal reserves of fuel.  Planing a flight with a 35% fuel reserve and then changing it en route to arrive with minimal fuel to spare would have me worried and I definitely would not be reporting "everything is OK".

rc

I think they did think they knew where they were.  The key word here is "think".  Even though they may have been off-course, they still had a reasonable level of confidence that they knew where they were in terms of arriving calculated LOP.  The problem (I believe) is a combination of other problems that they were completely unware of and had no way of detecting.  Such as a timing issue with chronometer - 1 second equals 1 mile correct?  Where was the last calibration - and how accurate was it?
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Erik

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Re: The flight plan, magnetic course, headwinds.
« Reply #62 on: January 02, 2012, 07:52:21 PM »

Very interesting discussion of some of the many variables that can figure into getting lost over the ocean - or finding one's way.

One thing that may help keep things clear is the independence of many airborne indication systems from mother earth and the universe itself: with the exception of magnetic compasses and RDF equipment (and today's GPS, etc.) other indications are based on what the airplane can sense from its environment.  An airplane is not a car on a pavement - without outside observations of earth, stars, etc. airspeed and headings provide for no more than dead reckoning.  Dead reckoning is subject to drift, headwinds and tailwinds, etc.

Gary's done a great job of describing how both the airborne sensing and external observation elements fit, IMHO, and as a flight instructor he knows them quite well.  He's also done a great job of giving clarity to great circle and how its application varies with the latitudes - and why it was negligible in the Lae - Howland case.

He has also ably demonstrated why being off-course mid-route is not such a danger or penalizing thing:

GL -
"For example, flying 2556 SM from Lae to Howland, if you wandered off course 100 SM at the midpoint of the flight it would add only 8 SM to the total route, only three minutes and twelve seconds to the flight. If you find yourself off course you don't make a large change in your heading to get back on the course line that you had drawn on your chart but change heading to head directly towards the destination..."

What needs to be considered also is awareness of that error at an early enough time to correct for it - Gary's statement "...If you find yourself off course you don't make a large change in your heading to get back on the course line..." is a reminder that timely awareness of the error is crucial if one would avoid the need of major correction at the end of the course line.  "IF" becomes a large word.
Any number of things can lead to such a large mid-course error - and any number of things can prevent its detection.  Most simply perhaps is finding one's self unable to get reliable information from outside the airplane - fixed points on mother earth or in the heavens, for example.  Then one is reliant on the airborne sensing as mentioned - proceeding by mag heading and nothing but airspeed and assumptions from forecasts as to winds, and therefore assumptions about speed over the ground.  The later that detection is made, the greater the penalty that must be overcome; if not detected with certainty by the end of the course line, one is "lost".

All very interesting.  There are so many variables that could have played into AE's and FN's predicament - including the possiblity of unrealized error mid-course and finding themselve with a fairly large penalty - perhaps even of unknown direction - at the end of the course line. 

Like most accidents, some combination of things likely conspired to deliver the pair into a loss situation at the end of that line - it could have been instrument error, it could have been a lack of sufficient readings from outside fixed objects for any number of reasons, or a combination of such things.

LTM -

You got it Jeff!

What needs to be considered also is awareness of that error at an early enough time to correct for it - Gary's statement "...If you find yourself off course you don't make a large change in your heading to get back on the course line..." is a reminder that timely awareness of the error is crucial if one would avoid the need of major correction at the end of the course line.  "IF" becomes a large word.

"If" is a very big word.  And your,  "... at an early enough time... " comment is also golden.  That can't be overstated enough!

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Gary LaPook

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Re: The flight plan, magnetic course, headwinds.
« Reply #63 on: January 02, 2012, 09:21:08 PM »

Certainly some new instruments fail and almost always in the first few hours. If they don't fail then then they tend to last a long time. Earhart's instruments were well "broken in" but not old enough to have suffered much wear.

Airplanes of that era often had venturis to provide vacuum sources but I can't see any in any of the photos of the plane so it must have incorporated vacuum pumps, one on each engine because one pump wouldn't have provided enough suction for all the gyro instruments in the plane. In addition, they even understood the idea of redundancy back then.

There was a vacuum gauge too to detect leaks in the vacuum system, to make sure that the vacuum pumps sucked enough.

There was a DG that was part of the autopilot so it was not a simple "wing leveler."
« Last Edit: January 24, 2012, 11:41:59 PM by Gary LaPook »
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Harry Howe, Jr.

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Re: The flight plan, magnetic course, headwinds.
« Reply #64 on: January 02, 2012, 09:37:33 PM »


And how about Fred?  Did he fall off of the wagon?
In the Brines Letter  Tighar Archived Docunents, the Brines Letter, He Brines, referred to FN as "a six bottle man" and intimated that FN had enjoyed the Lae nightlife while they were there and had to be poured into the plane for takeoff. 

If true, how much sobering up and hangover time might have been involved during the flight?  Did FN have some bottles of his favorite liquid refreshment in his kit-bag?
No Worries Mates
LTM   Harry (TIGHAR #3244R)
 
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richie conroy

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Re: The flight plan, magnetic course, headwinds.
« Reply #65 on: January 02, 2012, 10:39:59 PM »



http://earchives.lib.purdue.edu/cdm4/item_viewer.php?CISOROOT=/earhart&CISOPTR=3126&CISOBOX=1&REC=10

Notes concerning sun’s course on line of flight, as used by Fred Noonan in navigation, to aid in search, ca. July 1937
We are an echo of the past


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« Last Edit: January 02, 2012, 10:41:46 PM by richie conroy »
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Martin X. Moleski, SJ

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Re: The flight plan, magnetic course, headwinds.
« Reply #66 on: January 02, 2012, 10:40:02 PM »

Where was the last calibration - and how accurate was it?

"Delayed in Lae."
LTM,

           Marty
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Gary LaPook

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Re: Question about the Ontario
« Reply #68 on: January 03, 2012, 01:16:53 AM »


Although there were no radio exchange between the Ontario and AE, could Noonan have used some type of spotting scope to visually verify that it was the Ontario? Could this have been easily done at 8 sm out at 8,000ft?
It was night and dark, no moon. Ships are dark things at night, it is amazing that a ship could be spotted at night, was the Ontario shining a spot light?

gl
« Last Edit: January 03, 2012, 08:01:00 AM by Martin X. Moleski, SJ »
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Gary LaPook

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Re: The flight plan, magnetic course, headwinds.
« Reply #69 on: January 03, 2012, 01:35:32 AM »

Quote
If ground speed airspeed turns out to be in error, then wouldn't that have caused Noonan to possibly calclate the wrong wind corrections too?


Now why the navigation itself might have failed, that is a different story. I am inclined to believe that they were entering cloudy conditions after spotting the Ontario that worsened as time went on. If we assume that to be true, they might have used DR all the remainder of the trip (1277 miles). As daybreak came, even if the conditions improved from overcast, the stars might have been impossible to spot. So I think it is quite possible that they did not find another reference after spotting the Ontario. What is the magic number again? 10% of 1277 miles? Does this suggest that they were off by a maximum of 127 miles? That is quite a large hole if you ask me. Forced to guess, I would say they were at a minimum of 40 miles off target since they did not spot the Itasca mast or the smoke she was laying out for them that stretch out 10 miles (although I would still like to hear an estimate of how high that smoke rose in the 8mph cross wind).

I guess you missed my prior post, here is the relevant portion:

--------------------------------------------------------------

"The whole reason that Earhart hauled Noonan all the way around the world was so that he could get fixes to eliminate any errors that would have resulted from dead reckoning alone. This was also the reason, in the original planning, to take two navigators for the leg from Hawaii to Howland so that they could use their skill and equipment to find that Island. Note also, that they had recognized and decided that even the much shorter leg from Hawaii to Howland (only 1900 SM instead of 2556 SM) was too long to complete with only dead reckoning. If Earhart wanted to dead reckon that leg then there was no reason to incur the expenses of having two navigators on board, Earhart could have done the dead reckoning herself as she had done when flying solo across the Atlantic and when flying solo from Hawaii to California. All the planning for the World Flight was based on the knowledge that dead reckoning was not sufficiently accurate for the most difficult leg of the flight, that of locating Howland, coming either from Hawaii or from Lae.  The original plan was for Noonan to leave the flight at Howland and Manning to leave at Darwin with Earhart flying the rest of the flight solo. This is conclusive proof that they knew that finding Howland was THE most critical part of the entire around the world flight

I have attached Earhart's June 30, 1937 radiogram. It requested weather information because " FN MUST HAVE STAR SIGHTS."

In prior posts I have demonstrated how Noonan computed a "point of no return" (PNR) which allowed them to fly until 1407 Z and to within 817 SM of Howland and still be able to return to Lae. Since it is highly likely that Noonan knew of the location of the Rabaul airport after talking to the people at the Lae airport that was 400 SM along the course line to Howland. (And also, very likely, Noonan and Earhart had talked to pilots arriving from Rabaul.) Noonan would have calculated a PNR for a departure from Lae with a return to Rabaul. Since Rabaul was closer to Howland, this PNR would also be closer to Howland. Doing this calculation we find the PNR occurs at 1526 Z, 1901 SM from Lae, only 655 SM short of Howland (only 55 SM short of Tabiteuea in the Gilberts) and only three hours and forty-five minutes before the 1912 Z radio report of "must be on you" from Earhart. So if Noonan had not been able to get fixes they could have turned around and returned safely to Lae or Rabaul from nearly over the Gilberts and try again another day.

Do we know that Noonan knew how to calculate a PNR and that his practice was to do this calculation? Yes. On the departure from Hawaii to Howland on March 20th they took aboard an extra 75 gallons of fuel to allow a return to Hawaii after flying for 8 hours on the leg to Howland. This meant that they would have flown 1320 SM and would have come as close 580 SM to howland before turning around. This extra fuel was taken aboard after Noonan calculated the PNR based on having to fight a headwind on the return leg to Hawaii, this is the standard PNR computation...

So now the creators of this "Monte Carlo Simulation" take the position that in spite of all the expense and careful preparation and Noonan's prior careful calculations including calculating PNRs that after all that, flying almost all the way around the world, that at the critical moment Earhart and Noonan just decided to ignore all the prior planning and just said "AHHHH, let's just go for it!"

----------------------------------------------

The point of no return was far past the Ontario, almost to the Gilbert Islands and they could have turned around and returned to a safe airport until the PNR. In the past Earhart had turned around and she planned on that possibility on the originally planned flight from Hawaii to Howland so there is no reason to think they wouldn't do it this time if Noonan couldn't get star sights.

gl
« Last Edit: January 03, 2012, 01:40:07 AM by Gary LaPook »
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Gary LaPook

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Re: The flight plan, magnetic course, headwinds.
« Reply #70 on: January 03, 2012, 02:09:33 AM »

Quote
If ground speed airspeed turns out to be in error, then wouldn't that have caused Noonan to possibly calclate the wrong wind corrections too?

Erik, at this point I think it is difficult to know for sure whether or not achieving the 124.5 mph ground speed was intentional or not. As they made their way around the storms East of Lae, it probably did not matter what ground speed was achieved during the diversion. They flew far enough South and high enough (10,000ft) to make sure they avoided the storms. We know that two legs of this journey was 909 miles and the ground speed was 124.5 mph. I recall reading that Fred had estimate the head winds at 23 knots before he left Lae and this did not change after they had a visual on Nukumanu Island.
The 23 knot wind was measured in flight by Noonan using his drift meter and that was reported by Earhart to Lae at 0718 Z. We know it was determined by dirft meter because the other way to measured the wind in flight over the ocean is to get two celestial fixes and compute what the wind was between these fixes and that wasn't available because the flight had been flying in daylight so Noonan couldn't shoot the two stars needed for a fix.  See how to determine wind in flight here. Also see what Noonan wrote about using a drift meter here. Also see what Noonan wrote about measuring the in flight winds between fixes in his letter that I have attached. Here is a link to an example of celestial navigation in flight that includes working out the winds between fixes.
Quote


From my perspective, once they flew over Nukumanu Island and intercepted the flight path, approaching the end of a segment in the flight plan and they were right on the line, this was probably not by accident. I would have expected them to them resume their original flight plan that did include achieving a 150 mph ground speed going forward regardless of the 23 mph head wind. AE announced her altitude, and headwinds, so it is a bit of a mystery why they would continue at a reduced speed unless there was some other concern or perhaps an equipment malfunction that was undetected. I cannot believe he just poked through the Lockheed documents and thought that this 124.5 mph ground speed was an ideal speed. There was no time to re-compute the entire flight plan on a whim and I have not heard any evidence that he would make such an attempt.

It was 23 knots, not mph, the wind was 26 mph.
The problem with increasing airspeed to maintain the planned ground speed is that the fuel flow increases at a faster rate than the increase in the airspeed so the specific range goes down and they run out of fuel sooner. If that is your theory then that explains why she ran out of gas shortly after her last transmission at 2013 Z. You should be pleased that Elgin Long agrees with you.
Quote

Another factor that I have been thinking about is that once they departed Nukumanu Island, this was about 0718GMT and I do not believe the sun had set at that point in time. They proceeded 3.2 hours after leaving Nukumanu Island before spotting the Ontario, how much time did that provide for Noonan to perform his celestial navigation? That would be interesting to know.

The sun was just setting at 0718 Z in the vicinity of Nukumanu and twilight lasted 25 minutes in that latitude and time of the year so Noonan would have had 2.8 hours to shoot stars after it got dark enough.

gl
« Last Edit: January 03, 2012, 03:41:17 AM by Gary LaPook »
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Gary LaPook

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Re: The flight plan, magnetic course, headwinds.
« Reply #71 on: January 03, 2012, 03:31:44 AM »


There is a bit of a problem here from what I can see so far as the time stamps in the Lae radio log is concerned. The time between reports was only 2 hours yet they traveled 652 miles. For this to be true, they would have had to be traveling 326 MPH (ground speed) between check point A and check point B. This must be incorrect. If we assume that perhaps the first time stamp is incorrect but the second time stamp is correct (7 hours and 18 minutes since departing Lae), this would produce an approximate ground speed of 124.5 mph from as they progressed from Lae to check point A and then to check point B. If we now make the assumption that until check point B was encountered, and a land reference was used to estimate air speed, they were not adjusting for head winds. If we make this assumption, and we add the 23 knot head wind, this works out to an airspeed of 151 mph (at sea level), and a rough estimate of 126 mph indicated airspeed at 10,000ft (2% per 1000 feet).

If we now compare the actual flight plan to when they arrived at check point B, this was at a point about 890 miles on the original flight plan path that had assumed a ground speed of 150 mph, this works out to about 5 hours and 56 minutes en route on the original flight plan. This means that they were behind schedule, 1 hour and 22 minutes according to the original flight plan. What is also interesting here is that looking at the original flight plan, 890 miles out from Lae; they would have been in the 5 segment of the flight plan (assuming that they used the original Howland to Lae flight plan, reversed). This would have been at a point 155 miles out on a 175 mile segment. Assuming that they stayed on the same course and speed as they did from point A to point B, they would have intersected the original flight plan path in 33.2 miles or roughly within 16 minutes where the next segment in the original flight plan would begin.


You shouldn't fall into the trap of believing that the times that the coordinates were reported were the actual time at those positions. There is a standard format for oceanic positions reports that goes like this.

"Gander radio this is Cessna November one six two one seven;
Forty west forty three thirty five north at two zero one five;
Flight level one zero zero;
I-F-R;
Estimating thirty five west forty one twenty north at two two three zero;
Thirty west thirty nine zero five north next;
Over."

The time (Zulu of course) of the position is obviously an important element of the report and is the time at the position, not the time of the radio message which might be quite a bit latter depending on HF propagation conditions.

Earhart's report didn't follow this format, she didn't give the time they were at the reported coordinates. All we know about the time it took to get to Nukumanu is that it was more than 6:18 and less than 7:18, too late to report on the 0618 Z scheduled broadcast but early enough to include it in the 0718 Z scheduled broadcast.

Look at it another way, what are the chances that they were just west of Nukumanu exactly at the scheduled broadcast time?

If they were flying at 148 mph as recommended by figure I of report 487 (148 is a correction after reviewing the original document) and they had the 26 mph wind reported by them, then the average ground speed would have been 122 mph and the time  to Nukumanu would have been 6:57, twenty-one minutes earlier than the scheduled radio broadcast.

So compute your ground speeds with these facts in mind.

gl
« Last Edit: January 15, 2012, 12:46:20 AM by Gary LaPook »
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Gary LaPook

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Re: The flight plan, magnetic course, headwinds.
« Reply #72 on: January 03, 2012, 05:17:27 AM »



Either way, both systems were operating on the same vacum - correct?  What about a vacum "issue".  Even if not, and the autopilot was a "wing-leveler" only, then it wouldn't matter much.  It would essentially mean AE was flying by hand adjusting the "wing-leveler" to match DG.

Does anyone happen to have any details on the Electra's pitot/static configuration?  Vacum configuration?  Or more details on Noonan's compass?
But no possible failure of the vacuum system could affect the three compasses on board, two of which were aperiodic compasses. You have probably never heard of an "aperiodic compass" before. It has that name because it has no period which means that it is dead steady even in turns and stops on the new heading without any overshoot or any oscillations right or left. It was also called a "dead compass" because it was dead steady. It was developed for utmost accuracy in aircraft and allowed the pilot and navigator to maintain a steady course even without a DG. Normal "pilot's " compasses dance around a bit in flight and have many errors if the plane accelerates or turns which is the reason why the DG was developed in the first place, to provide a steadier heading reference when the pilot's compass was moving around. Many airplanes were not equipped with a DG but instead had an aperiodic compass which also provided a steady heading reference. So, as it turns out, Earhart didn't really need a DG, she could have used just the aperiodic compass mounted on the floor and Noonan also had one of these steady heading references so he could check on Earhart's piloting. They are also extremely easy to read without mistake because you rotate a bezel to the desired heading and simply keeping the plane heading so that the index in the compass is parallel with with the lines on the bezel keeps you on heading. See picture here.


gl
« Last Edit: January 03, 2012, 05:21:27 AM by Gary LaPook »
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Richard C Cooke

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Re: The flight plan, magnetic course, headwinds.
« Reply #73 on: January 03, 2012, 07:24:06 AM »

So Richard, if they thought they knew where they were then what happened???  Was FN working with AE?  Did they just miss Howland?
The plan was for FN to get them close enough for AE to home in on the portable radio beacon on Howland, but the beacon was not working because the battery had been drained and the lack of effective radio communication meant they were on their own.  They did not get close enough to see Howland, so they had to implement their alternate plan, and the group of islands and reefs to the SSE of Howland look like the logical place to head for.

rc
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Irvine John Donald

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Re: The flight plan, magnetic course, headwinds.
« Reply #74 on: January 03, 2012, 07:35:00 AM »

Thanks Richard

I agree that this was their plan. But this thread is suggesting why they missed and is suggesting it may have been hundreds of miles off plan. Would FN not have caught this?  This is what puzzles me. Nothing in the messages to suggest they are off course. Timing for arrival seemed right.  World class navigator who had so far helped to get AE around the world this far. And yet.....   Did they just not see Howland right below them or on the horizon?
Respectfully Submitted;

Irv
 
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