Malaysian Airlines MH370 contact lost
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Regarding the credibility of INMARSAT data
I have just seen an interview with a vice president from INMARSAT - after listening to this I must say that I have regained considerable confidence in the correctness of the data presented by INMARSAT in the case of the missing MH370.
Link:
MH370: Is Inmarsat right? - CNN.com
Link:
MH370: Is Inmarsat right? - CNN.com
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Two queries:
Woodpecker - is the 777 system such that an 'automatic' APU start would automatically bring the APU gen on line?
Anyone - have we seen any estimates of a/c radial groundspeed from the BFO data from Inmarsat? This would give the minimum g/s at any point, and as the a/c travels further from the satellite should approach actual g/s.
Woodpecker - is the 777 system such that an 'automatic' APU start would automatically bring the APU gen on line?
Anyone - have we seen any estimates of a/c radial groundspeed from the BFO data from Inmarsat? This would give the minimum g/s at any point, and as the a/c travels further from the satellite should approach actual g/s.
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Originally Posted by BOAC
Anyone - have we seen any estimates of a/c radial groundspeed from the BFO data from Inmarsat?
(*) EDIT: That applies in particular to the BFO value. The notes on page 2 of the Inmarsat release explain the factors that may affect the accuracy.
Last edited by Gysbreght; 8th Jun 2014 at 21:36.
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what else can they stuff up?
How can we have confidence in anything these so called experts undertaking this search tell us?
Sink rate therefore would have only been 11 fps . . . does not add up.
FWIW a clean 777-200 at light weights descending at say Vref 30 +80 (min clean) possibly needs an ROD of around 1000fpm/16 fps with engines at idle to a maintain min clean IAS. However if you chuck all the rules about buffet margins and min FCOM speeds out of the window due to "Force Majeur"/pilot incapacitation then low RODs become very credible and I think extrapolating "time to splash" from some (alledged ) datalink burst becomes highly speculative.
(777 driver with X thousand hours on type, so no doubt about to be moderated out)
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. A number the realtives of missing pax are in the process of launching a reward offer of $5m using the Indiegogo web site. Suspecting a cover up on the part of the authorities, they are hoping this sizeable reward
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BOAC and Gysbreght.
From the Inmarsat filed data you have for each ping: a time H, a BTO (a length of time), a BFO (a frequency value). Please, reread the first page of the "raw data".
The BTO is only used to know at which distance R is the a/c from the satellite at the time H. From this distance R you can know that the a/c is somewhere on a circle. This circle is the intersection of:
- The sphere centered on the satellite at the time H and with a radius R,
and
- the "sphere" centered at the Earth center and which has the radius of the Earth plus the a/c altitude. This "sphere" is not a true sphere because the Earth is not perfectly spherical, so the circle is not a true circle.
The BFO comes from:
-1- the speed of the a/c relatively to the satellite,
-2- the speed of the satellite relatively to the a/c,
-3- the speed of the satellite relatively to the Earth station,
-4- an "error" from the a/c component which communicate with the satellite,
-5- the position of the satellite relatively to its theoretical fixed position above the equator.
#3 and #5 are perfectly known at whatever time. #4 is deduced from the data of the begining of the flight and from older flights of the a/c. So the global effect of #1 and #2 could be known from the filed BFO.
Theoreticaly, the a/c compensate the BFO from its own speed relatively to the satellite (#1). But this compensation is based on a fixed satellite. So the compensation the a/c mades is wrong when the satellite is not at its theoretical position. Say this value is F1.
The other useful component of the BFO is the one from the satellite speed relatively to the a/c (#2). Say this component value is F2.
Only the sum F1 + F2 is known. It results from the measured BFO after two corrections: 1) for BFO due to the satellite speed relatively to the Earth station and 2) for the "error" from the a/c component deduced from BFOs at times when the a/c position was known before take off.
For a given point on the circle, you can know F2 (because the satellite speed value and direction are perfectly known at the time H). So you can deduce F1.
But, you can't deduce a speed of the a/c from F1, only a "couple" [speed + direction of flight]. There are an infinity of couples which are in accordance with F1, thus with the BFO, but you have a minimum speed (flight direction exactly away from the satellite) and a maximum angle between the direction of flight and the line of sight of the satellite given by the maximum speed of the a/c. This error is also very small, so the incertitude about the "couple" is pretty large.
Fortunately, there are two other constraints:
- you have to reach the next circle at the right time (the time of the next ping),
- the point reached has to be in accordance with the new BFO at this time.
If you knows the first point (from primary radar position extrapolation), it is easy to find a flight path in accordance with all data, after making suppositions about the speed of the a/c (for each one, different headings...).
If you dont't know the first point, you have to compute many hypothesis (about the first point) to find credible flight pathes.
From the Inmarsat filed data you have for each ping: a time H, a BTO (a length of time), a BFO (a frequency value). Please, reread the first page of the "raw data".
The BTO is only used to know at which distance R is the a/c from the satellite at the time H. From this distance R you can know that the a/c is somewhere on a circle. This circle is the intersection of:
- The sphere centered on the satellite at the time H and with a radius R,
and
- the "sphere" centered at the Earth center and which has the radius of the Earth plus the a/c altitude. This "sphere" is not a true sphere because the Earth is not perfectly spherical, so the circle is not a true circle.
The BFO comes from:
-1- the speed of the a/c relatively to the satellite,
-2- the speed of the satellite relatively to the a/c,
-3- the speed of the satellite relatively to the Earth station,
-4- an "error" from the a/c component which communicate with the satellite,
-5- the position of the satellite relatively to its theoretical fixed position above the equator.
#3 and #5 are perfectly known at whatever time. #4 is deduced from the data of the begining of the flight and from older flights of the a/c. So the global effect of #1 and #2 could be known from the filed BFO.
Theoreticaly, the a/c compensate the BFO from its own speed relatively to the satellite (#1). But this compensation is based on a fixed satellite. So the compensation the a/c mades is wrong when the satellite is not at its theoretical position. Say this value is F1.
The other useful component of the BFO is the one from the satellite speed relatively to the a/c (#2). Say this component value is F2.
Only the sum F1 + F2 is known. It results from the measured BFO after two corrections: 1) for BFO due to the satellite speed relatively to the Earth station and 2) for the "error" from the a/c component deduced from BFOs at times when the a/c position was known before take off.
For a given point on the circle, you can know F2 (because the satellite speed value and direction are perfectly known at the time H). So you can deduce F1.
But, you can't deduce a speed of the a/c from F1, only a "couple" [speed + direction of flight]. There are an infinity of couples which are in accordance with F1, thus with the BFO, but you have a minimum speed (flight direction exactly away from the satellite) and a maximum angle between the direction of flight and the line of sight of the satellite given by the maximum speed of the a/c. This error is also very small, so the incertitude about the "couple" is pretty large.
Fortunately, there are two other constraints:
- you have to reach the next circle at the right time (the time of the next ping),
- the point reached has to be in accordance with the new BFO at this time.
If you knows the first point (from primary radar position extrapolation), it is easy to find a flight path in accordance with all data, after making suppositions about the speed of the a/c (for each one, different headings...).
If you dont't know the first point, you have to compute many hypothesis (about the first point) to find credible flight pathes.
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Shadoko wrote
This is an important point. Further comments:
(1) Conceptually, it is tidier to separate out:
But, you can't deduce a speed of the a/c from F1, only a "couple" [speed + direction of flight]. There are an infinity of couples which are in accordance with F1, thus with the BFO, but you have a minimum speed (flight direction exactly away from the satellite) and a maximum angle between the direction of flight and the line of sight of the satellite given by the maximum speed of the a/c. This error is also very small, so the incertitude about the "couple" is pretty large.
(1) Conceptually, it is tidier to separate out:
(a) the velocity component along the axis between the satellite and the aircraft location (i.e. notional point at sea level below aircraft) due to satellite motion relative to earth. This component can be computed precisely for any given time and (assumed) aircraft location.
(b) the total velocity component along the axis between the aircraft and the satellite due to the combination of aircraft and satellite motion. This component is equivalent to the doppler shift between the aircraft and the satellite which contributes to the overall BFO value.
(2) The BFO correction value is apparently derived based on measurement of the frequency deviation of the incoming signal received from the satellite. The idea is that the a/c system pre-compensates for Doppler shift such that the signal received by the satellite appears at the nominal channel frequency.
Last edited by Communicator; 9th Jun 2014 at 05:38.
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Originally Posted by shadoko
but you have a minimum speed (flight direction exactly away from the satellite) and a maximum angle between the direction of flight and the line of sight of the satellite given by the maximum speed of the a/c.
Originally Posted by Gysbreght
the a/c system assumes the satellite to be at its nominal position and that error results in the BFO.
The APU fuel,feed is from the left wing tank. It uses either the FWD wing boost pump or a dedicated AC/DC APU fuel pump.
When Both AC BUS L and R are unpowered the APU is commanded to start. The APU door opens electrically, but the APU will start either electrically or pneumatically.
As an ETOPS airplane, the engines are normally staggered; ie., one of them is a higher time/cycles than the other. On our fleet, the right engine is the higher time engine.
Due to this stagger, the right engine normally consumes slightly more fuel, and would be expected to flameout first. In a fuel flameout situation, there would probably be less than a minutes worth of fuel in the APU fuel lines, probably just sufficient to light off, achieve power generation speed, then flameout. Hence the attempted logon.
When Both AC BUS L and R are unpowered the APU is commanded to start. The APU door opens electrically, but the APU will start either electrically or pneumatically.
As an ETOPS airplane, the engines are normally staggered; ie., one of them is a higher time/cycles than the other. On our fleet, the right engine is the higher time engine.
Due to this stagger, the right engine normally consumes slightly more fuel, and would be expected to flameout first. In a fuel flameout situation, there would probably be less than a minutes worth of fuel in the APU fuel lines, probably just sufficient to light off, achieve power generation speed, then flameout. Hence the attempted logon.
short flights long nights
The answer is yes.
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I have just seen an interview with a vice president from INMARSAT - after listening to this I must say that I have regained considerable confidence in the correctness of the data presented by INMARSAT in the case of the missing MH370.
Link:
MH370: Is Inmarsat right? - CNN.com
Link:
MH370: Is Inmarsat right? - CNN.com
Let's hope this puts the doubters to bed, he clearly stated (twice) the data had been vaidated against other 777 and this frame on previous flights (which rules out any anomolies with this planes satcom system).
The only disappointment was not asking him about the final ping, to have him put that on record.
It does raise the question for me if the TPL pings were not 370,what were they, was the conclusion reached that they weren't because no wreckage was found or for some other technical reason.
I guess we will know that when we see where the next search stage starts.
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oldoberon
Obviously this depends on the efficiency of Bluefin.
TIGHAR - the folks who believe they know where Earhart crashed have been extremely critical of Bluefin. However, I'm not certain of their level of expertise.
TIGHAR - the folks who believe they know where Earhart crashed have been extremely critical of Bluefin. However, I'm not certain of their level of expertise.
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No, BFO depends on the satellite speed and the airplane speed. The BFO sign does not reverse as the satellite moves through its apogee. If the airplane speed is constant in magnitude and direction, the rate-of-change of BFO changes gradually with the changing satellite speed.
Secondly, if I understand correctly (!!), there is a Doppler shift recorded by the ground station for each burst. Presumably this can be translated into an apparent radial 'ground speed' which can then be corrected by the BFO to produce a reasonbly accurate minimum 'ground speed'. Are these values available?
I have been struggling with the various arguments for choosing the southerly arc in preference to the northern one. It seems to me that the doppler/BFO shift is due to the instantaneous rate of change of the path length between the aircraft and the satellite combined with the instantaneous rate of path length between the ground station and the satellite, This same path length rate of change is what has driven the distance between the arcs at the hourly time intervals, ie I can't see how the two bits of information are sufficiently independent of each other to tell whether the southern or northern arc is a better fit.
Also, I have not seen any mention of windspeed or direction. If the aircraft has flown for 6 hours from it's last known positive position would not the speed (and probably the direction) have been influenced by the path passing through different weather patterns thus messing up the "assumed" speed and track constancy?
Lastly, can someone point me to some figures for the actual speed of the satellite relative to it's nominal geostationary position? Is the speed significant relative to the airspeed of a 777 or even relative to the likely winds seen at the assumed altitude of the aircraft in that area of the world?
Also, I have not seen any mention of windspeed or direction. If the aircraft has flown for 6 hours from it's last known positive position would not the speed (and probably the direction) have been influenced by the path passing through different weather patterns thus messing up the "assumed" speed and track constancy?
Lastly, can someone point me to some figures for the actual speed of the satellite relative to it's nominal geostationary position? Is the speed significant relative to the airspeed of a 777 or even relative to the likely winds seen at the assumed altitude of the aircraft in that area of the world?
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Originally Posted by rans
Lastly, can someone point me to some figures for the actual speed of the satellite relative to it's nominal geostationary position? Is the speed significant relative to the airspeed of a 777 or even relative to the likely winds seen at the assumed altitude of the aircraft in that area of the world?
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Meaning of BFO Data
Kudos to everyone for finally publishing the Inmarsat "raw data". (BTW - Inmarsat is, of course, bound by its clients' instructions. MAS finally authorized the release of the data.)
Based on a basic understanding of the electronics involved (Inmarsat Classic Aero mobile terminal), the fact that this equipment has been around since the 1990s, and discussions of the "BFO" data (e.g. on Duncan Steel's website), it appears that the BFO values are the amount of Doppler-shift pre-compensation applied by the a/c terminal.
This implies that the BFO value is measured by the a/c terminal and then transmitted as part of the Satcom data to Inmarsat for diagnostic purposes. This makes eminent sense since Doppler shift is a major reason for degradation and failure of the a/c-satellite-earth station links.
Thus, the BFO value is proportional to the relative velocity of the satellite and the a/c along the LOS (line of sight) axis between them.
Still unclear is the precise correlation between the relative LOS velocity and the amount of the BFO change. What LOS velocity (in knots) requires a a Doppler shift pre-correction of 100 Hz? Why are the amounts (apparently) never negative?
It may be that the frequency offset relates to a base frequency equivalent to 600 MHz, rather than the uplink frequency of 1600 MHz. This could make sense depending on exactly how the satellite deals with Doppler shift encountered on uplink and downlink transmissions.
Based on a basic understanding of the electronics involved (Inmarsat Classic Aero mobile terminal), the fact that this equipment has been around since the 1990s, and discussions of the "BFO" data (e.g. on Duncan Steel's website), it appears that the BFO values are the amount of Doppler-shift pre-compensation applied by the a/c terminal.
This implies that the BFO value is measured by the a/c terminal and then transmitted as part of the Satcom data to Inmarsat for diagnostic purposes. This makes eminent sense since Doppler shift is a major reason for degradation and failure of the a/c-satellite-earth station links.
Thus, the BFO value is proportional to the relative velocity of the satellite and the a/c along the LOS (line of sight) axis between them.
Still unclear is the precise correlation between the relative LOS velocity and the amount of the BFO change. What LOS velocity (in knots) requires a a Doppler shift pre-correction of 100 Hz? Why are the amounts (apparently) never negative?
It may be that the frequency offset relates to a base frequency equivalent to 600 MHz, rather than the uplink frequency of 1600 MHz. This could make sense depending on exactly how the satellite deals with Doppler shift encountered on uplink and downlink transmissions.
Last edited by Communicator; 9th Jun 2014 at 21:04.
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N to S satellite motion identifies southern track.
Geostationary satellites have typically been station kept in 40 mile boxes since 1972. To save Reaction Control System fuel Inmarsat allowed inclination of the orbit to grow. This resulted in ~700 miles of N-S motion of the satellite during 7 hours of observations. The Burst Frequency Offset value matched in value and sinusoidal rate of change consistent with a 24 hour orbit. The satellite motion was then removed from the observed doppler which generated a vector to resolve the N S ambiguity on the line of position generated by the range measurement. Further Doppler signature analysis bracketed the speed and heading of successive handshakes. Doppler analysis was used for decades by SARSAT albeit with much more orbital inclination but less stable frequency ELT's. Inmarsat deserves credit for figuring it out, and VP Mark Dickinson for explaining it on CNN.