Flight 370 and the Flight Recorders: The Truth

Linda Moulton Howe's consultant Mark Wood has provided with a great deal of valuable information about the Malaysian Airlines Flight MH370 mystery. Below is his analysis of the actual situation regarding the flight recorders, the great majority of it material that you will not find in the media. For more reporting like this from Linda and Mark, go to

Captain Mark Wood is a retired U.S. Navy Captain, P-3 Mission Commander and Tactical Coordinator and former Ocean Engineering Instructor at Florida Atlantic University, Department of Ocean Engineering.

Here is Mark's report:

I am finding a lot of the reporting very interesting with regard to the reports of several ships having picked up possible “pings” associated with the Underwater Location Beacons (ULB) attached to MH370’s Flight Data Recorders. What seems to be lacking is a total lack of facts related to the operational specifications of the units as well as the underwater acoustics that govern the transmission of the location signals “pings” and the ability of the ships to receive them and more importantly home in on them. The following web link from the Australian Transportation Safety Board (ATSB) has a pretty good list of specifications that are required by EUROCAE and subsequently ICAO for this equipment, and I think it is important to first look at what these boxes can do, and for how long.

Since the vast majority of airplane accidents occur over land, the primary concern is the survivability under extreme impact loads and the resulting heat from fuel fires. Here are the required specifications:

The crashworthiness standards of flight recorders was revised in 2003 by the European Organization for Civil Aviation Equipment (EUROCAE) committee, an international body on which the ATSB was represented. The recorder’s memory module is now required to withstand:

an impact producing a 3,400-g deceleration for 6.5 milliseconds (equivalent to an impact velocity of 270 knots and a deceleration or crushing distance of 45 cm)
a penetration force produced by a 227 kilograms (500 pounds) weight which is dropped from a height of 3 meters (10 feet)
a static crush force of 22.25 kN (5,000 pounds) applied continuously for 5 minutes
a fire of 1,100 degrees Celsius for 60 minutes.

The key number here as it relates to a crash into a body of water is the static crush force which is specified to be 5,000lbs. Since seawater pressure increases 1 atmosphere (14.7psi) for every 33 feet of depth, 5,000lbs static crush force will be reached at @340 atmospheres which equates to @11,225 ft. of depth. If you then look at a potential flight path from Sumatra to the Southwest down off the coast of Australia that is defined by the “southern arc” that was proposed by INMARSAT as the most logical direction for MH370 to have flown, with the exception of the near shore coastal waters off Sumatra, the deep ocean depth from Sumatra to a position of about 26° S Latitude increases to about 17,000 feet and then beginning at about 26° S decreases to 12,000 feet deep. Between 30° S Latitude until the OB Trench at 32° S Latitude, the depth decreases to about 8,000 ft. to 11,000ft and then once past the trench dips down to below 12,000 feet to 14,000 feet deep. The key fact here is that for the majority of this track, the static pressure will cause the FDR to implode. Since the data is recorded on solid state chips, and no longer on magnetic tape or metal discs, the chances are good that the data can be recovered however. In one area specifically near the Batavia Seamount, the depth is actually less than 8,000 feet which would indicate if the crash were there, the box itself would survive, assuming the integrity was not compromised by the initial impact. This seamount is located at @ 26° S, 100° E, which is in the vicinity of the Chinese ship that heard a ping at 25° S and 101° E.

The second component of interest is the Underwater Location Beacon (ULB) which is attached to the FDR. It is battery powered and designed to begin operation when it detects that that it has been submerged in water (either fresh or salt).

When the ULB is immersed in water, it will begin to radiate an acoustic signal which can be received and transformed into an audible signal by a receiver. The ULB is sometimes called a 'pinger' due to the audible signal created by the receiver.

The ULB must meet the following requirements:
nominal operating frequency: 37.5 kHz
size (typical): 9.95 cm long by 3.30 cm diameter
operating depth: 0 to 6,096 meters (20,000 feet)
automatic activation by both fresh and salt water minimum operating life of 30 days. The acoustic output will decrease as the battery voltage decreases. It may be possible to still detect the ULB after 60 or more days but the detection range will be decreased.

The ULB can only be detected by a receiver under the surface of the water. The maximum detection range of a ULB is typically up to 2 to 3 kilometers but is dependent on:
ULB acoustic output level
receiver sensitivity
whether the ULB is buried by debris (e.g. aircraft structure and mud)
the ambient noise level (e.g. sea state, nearby boats, marine animals, gas and oil lines)
water temperature gradients
depth difference between the ULB and the receiver.

This is where things get interesting. The maximum specified range is @ 2-3km which is 6,652 feet to 9,843 feet which isn’t enough power to reach the surface in water that is greater than 10,000 feet. On first glance, this would seem to indicate that at the very least, if the “pings” they reported are in fact from the MH370 ULB, the FDR must be in water less than 10,000 feet deep since the Chinese boat was using a handheld receiver that they held over the rail to some limited depth, and not one of the more sophisticated deep water towed vehicles that the U.S. Navy has sent to the area.

Having made the above statement about receiving range, the real issue that is going to complicate things is how acoustic signals propagate underwater. Marine scientists and engineers who use acoustics in their research, or Navies that track submarines using underwater sound utilize a method called “ray tracing” to localize the source of a signal, whether it is a “ping” from a location device, or the mechanical sound from a submarine propulsion system or mechanical components, or the biological sounds from whales. “Rays” moving outward from a source do not always move in a straight line in the vertical plane. They will gradually curve or arc up or down in the direction of “decreasing” sound velocity. Since the velocity of sound in seawater is a function of temperature, pressure and salinity, the rays will tend to arc both up and down depending on the dominant variable.

For example, temperature tends to be relatively warm and constant in the shallow upper surface (300ft) due to mixing caused by wind, waves and warmth generated by sunlight. But as you go deeper, temperature tends to decrease until it reaches a constant temperature. At this point, since sound decreases with decreasing temperature, rays will tend to arc away from the surface towards this velocity minimum as temperature dominates. But once temperature becomes constant, and depth continues to increase, pressure becomes the dominant variable. Since velocity increases with increasing pressure, the deeper you go, the sound rays arc back up to the depth of minimum velocity, where pressure overtook temperature as the dominant variable. Thus sound rays will arc down in a gradual curve and then level out and arc back up and so on and so on. This phenomenon is called the “Deep Sound Channel” which has as its horizontal axis at the depth of minimum sound velocity.

The reason why this Deep Sound Channel is important is that sound can travel great distances within the channel so if a sound channel is closer to the bottom in an area where there is a seamount for example, instead of a sound source like a ULB sending a signal straight to the surface from its location, the sound may propagate within the channel and be picked up a greater distance from the source than the 2-3km maximum straight line distance from the source to the surface. As a result, it becomes a little more difficult to locate the object which is “pinging”. Now add the fact that once 30 days is reached, the battery power begins to die, and the range of the ULB will begin to decrease. In fact in many areas of the deep ocean, the arcing sound that comes back to the surface where ships and sonobuoys are used to detect submarines, will come back to the surface in multiple rings (remember, sound is omnidirectional) that can be separated by 20 or 30 miles. So tracking a sound source can be difficult and it takes an experienced acoustician to be able to locate a source when sound channels or convergence zones come into play.

I guess my point is that assuming the signals received by the vessels were from MH370, it doesn’t mean it is going to be easy to find. The fact that two ships, not co-located, received pings tells me that they may in fact be receiving signals from a sound channel or a convergence zone which will severely complicate the process of locating the source. More importantly, if their receiving equipment is omnidirectional as well, and does not have the ability to generate a direction in which the sound was received, it will almost be impossible for them to locate the source until more sophisticated equipment gets on scene. Now add to the fact that the range is going to begin to continually decrease day by day since it has been 30 days since the disappearance, and the ULB’s are only specified to operate at full power for 30 days, and the odds are less than even they will find the wreckage before the batteries die.

The other thing that points to the fact that they may be picking up a convergence zone or sound channel signal is that they have not recovered any floating debris associated with the aircraft. Since the disappearance occurred on the 8th, that means that it has been some 720 hours since it could have gone in the water. Even with a slow 1kt or 1.5kt current, any debris could be 700 to 1000 nm away from the impact.

With regard to your question as to a submarine “muddying the waters”? If I didn’t want the true location of the aircraft to be found, it would be relatively easy to just fly out into an area where you wanted everyone to think the aircraft had crashed, and drop a few ULB’s into the water separated by some distance and let everyone go crazy trying to locate them. It would be like trying to find a needle in a stack of needles. I am not saying that is what is happening, but it is a lot cheaper than sending a submarine into the area.

And again, our “model attractive” but unbelievably empty talking heads in the mainstream media are barking like trained seals waiting for someone to throw them another fish. Edward R. Murrow must be spinning in his grave.

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