- my point. What prevents detemination of the first from the measured Doppler shift? Obviously if the following is correct, this does......

- if I read you correctly, you are saying that any Doppler shift is PURELY due to satellite motion away from geo-stationary and not aircraft speed? I had understood from all the previous stuff about BFO that it was affected by aircraft ground speed. Now I am told that a/c speed is removed from the equation? Would this not result in a reversal of BFO sign as the satellite 'turned' on its path? Is this apparent in the published BFO data? Can you highlight it?

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.

The question was:
"is the 777 system such that an 'automatic' APU start would automatically bring the APU gen on line?"

The answer is yes.

thank you for link.

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.

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.

- this is all very confusing for a simple pilot! As the satellite reverses from its northbound travel to southbound travel I cannot see why the 'error' (the BFO?) caused by the rate of change of displacement from geo-stat does not reverse since the rate has reversed? Looked at another way, why is the BFO not zero as the satellite reaches 'apogee' and the satellite 'speed' wrt geo-stat becomes zero?

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?

- I believe I saw somewhere it moves 1.67 degees north and south over 24 hours. If you have the brainpower, you can work out the speed (probably a sinusoidal function) at that radius from the earth. Good luck..........

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.

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.:D

Previously in this thread, I described how it was possible to use the offset detected at the AES Rx of the SAT P channel carrier to pre-compensate the AES Tx frequency in the opposite direction, so that the SAT Rx always received the AES on the assigned channel frequency.

It now transpires that the Honeywell SATCOM package installed on 9M-MRO used a software algorithm to calculate the Doppler shift correction to be applied, based on the aircraft position and motion. However, the software assumed that the SAT was actually at its geostationary position of 0° 64.5°E and didn't take into account the eccentric ellipse of +/- 1.63° about the equator performed by the SAT in a siderial day.

Its this eccentric motion which is used by Inmarsat to differentiate whether the aircraft was on a Northern or Southern vector.

So, in this case the BFO is the difference between what the AES calculated, and what it would have calculated if its software used the actual SAT ephemeris values.

The "fly by wire system" has dedicated batteries that keep the computers powered during short power interruptions. These "dedicated FBW batteries" are normally kept charged by battery chargers powered by the AC generators.

All AC bus-bars loose power with associated generator failure until the other (or, if running, the APU) generator restores AC power (ignoring the limited AC produced by the static inverter)

However, never in all my years understood why they are called AC generators, not alternators!!

How is BFO Measured?
 

Jun stated:
I agree (and also previously stated in less detail) that pre-compensation values could readily be derived from observed Doppler shift in the download signal received from the satellite.

The idea that the BFO is pre-computed based on aircraft location, heading and velocity has recently been mentioned with some frequency here and elsewhere. The approach is certainly possible, but it seems vastly over-complicated (and thus error-prone) as a solution to the Doppler compensation problem compared to measuring the downlink Doppler shift.

Also, what is our basis for thinking that this is ACTUALLY happening in the Aero Classic units?

Just as importantly, given that Inmarsat, Duncan Steel and others used the BFO values essentially as a proxy for aircraft velocity (subject to some adjustments for three-dimensional heading), the residual error due to movements of the "geostationary" satellite (and uncompensated by the postulated pre-computation system) fails QUANTITAVELY to account for the observed values in the 100Hz - 350Hz range.

Given the cost of some of the underwater search assets involved, it would seem to be less expensive to charter 2-4 777s with similar satcom installations, wait for an approximately similar moon phase, maneuver the necessary satellite(s) to a similar orbit, and fly the chartered jets along the most likely routes both north and south to generate results for comparison. Even with compensating Inmarsat for maneuvering fuel it would seem to be a more productive use of resources.

Just read the notes on pages 1 & 2 of the Inmarsat data release. In part -
The permanent offset you are referring to, is as a result of Inmarsat creating a "nominal terminal" outside of the satellite.

ABC (Australia) news also reporting that Australian and Malaysian authorities are "negotiating" on who will pay for the search effort.

australia signed a contract with fugro survey from the netherlands to map the entire seafloor in the search area. ( 60000 square kilometers )


in german :


Flug MH370: Niederländische Firma soll Meeresboden kartieren - SPIEGEL ONLINE


english :


MH370: Australia appoints Fugro for bathymetric survey of search area - Nation | The Star Online

@lostinp
These guys are not searching for the plane, they are mapping the ocean depths in the search region to aid the upcoming sidescan sonar search from August onwards.

The tender is still open (until the end of June) for the bottom survey to locate the plane.

thommo101
Quote:"These guys are not searching for the plane, they are mapping the ocean depths in the search region to aid the upcoming sidescan sonar search from August onwards.

The tender is still open (until the end of June) for the bottom survey to locate the plane."

This video (from a Fugro employee) indicates it "may" be possible to locate the wreckage. They found a shipwreck in the Mediterranean, 9,000ft down, using sonar.

How deep is the Flight 370 search zone? ? Anderson Cooper 360 - CNN.com Blogs