One question a lot of people are asking in the wake of the Malaysia Airline Flight 370 tragedy (yet to be resolved as I write this), and the resulting mystery as to its fate, is why don’t flight data recorders (called “black boxes”), have bigger batteries? In many cases a crashed aircraft can be relatively easily found, especially if the crash was on land or near shore. However, as this case demonstrates, an aircraft lost in the deep sea can take months, and the battery in current black boxes only last weeks. What should we do?

Sadly, any change would have to wind its way through the regulatory and commercial process of adoption, and also require significant engineering effort to upgrade the related systems and redesign the packaging to accommodate and protect a larger battery, but we will not address these issues here. Let’s just concern ourselves with the issue of how to improve our oversight on airplane crashes so we can prevent (or at least significantly reduce) their recurrence. The biggest issue involved is the recovery of data from the aircraft after the fact.

Data recovery is a problem other vehicular black-box systems do not share, as they occur on known and explored land and can be easily recovered. Sea vessels, having had to deal with disaster management far before any autonomous systems (or even radio) existed, have long ago developed their own multiple-redundancy processes and technologies for both dealing with and recovering from catastrophic situations. Only in aircraft do we have the potential need to search through woods, mountains, and seas for the data package that would tell us the fate of the passengers and crew.

But would putting in a larger battery be the best solution? This has come up in the debates going on in the industry and legislature, as it has become apparent to all that even in a busy world very large things can fall through the cracks without proper oversight. A larger battery in the black box would enable the search for Flight 370 to go one for longer, increasing the chances that the aircraft wreckage would be found. Larger batteries in all black boxes would give us that much more time to find that vital information in the future.

However, that just increases the chances of finding the recorder, it does not guarantee that the box will be found. It is an appealing and intuitive solution to a very real problem, but it is a solution based on last-century technology. We need a solution that will not only prevent what is going on with Flight 370 from ever happening again, the solution should also bring with it modern real-world added value due to its advanced nature.

The best (but recognizably costly, but how much is safety worth?) solution would be to put aircraft into the Cloud. If every aircraft streamed its location, status, and other significant parameters while airborne, this situation would not exist, and we would know everything important about what happened to Flight 370. (Remote control to eliminate any hijacking or pilot-incapacitation issue would be an option worth looking into as well.)


Why not make the batteries last longer? There are three ways I can think of to approach this problem. First, we can make the data recorder beacons draw less power. Unless we assume that the beacons aren't very efficient, the only real way to get more broadcast time is to weaken the signal; it's straight physics. Making the recorders harder to find would at the very least offset any gains from making the broadcast longer. They already aren't specced to reach the surface from the depths of the sea floor in the primary MH370 search area, so reducing the signal strength would reduce the areas of ocean where the FDR would be findable or significantly increase the difficulty and cost to do so.

Second, we could have the batteries last longer. Absent a significant change in battery technology, the only really feasible way to do this to make the batteries bigger. The question then becomes 'how much bigger?' On top of that, there are many factors that have to be taken into account. Every kilogram that we make the recorders heavier means additional fuel burn (space likely isn't a problem directly) on every single flight taken by every aircraft carrying one. Although that doesn't sound like a lot, let's multiply it out.

Let's take some notional data. One performance chart for the Boeing 777-200 - same basic model as MH370 - states that the delta for fuel burn between a 'low' cargo weight and a 'high' cargo weight - a difference of 12 tons - is 2,962 Kg of fuel on a London-Dubai route. Jet-A is approximately 0.81 Kg/liter, so that means it's 1.23 liters/kg. So, 12 metric ton cargo weight differential results in a 2.962 metric ton difference in fuel consumption. Thus, 12000 / 2962 = ~4.05 Kg cargo/Kg fuel, or 0.247 Kg of fuel burn per Kg. of cargo. 0.247 Kg / 0.81 Kg/liter = 0.305 liters of additional fuel burn per Kg. of additional weight carried. That doesn't sound so bad. Jet-A this month is averaging about $5.48/gallon; since there are 3.79 liters/gallon that means $5.48/3.79 = right around $1.45/liter of Jet-A, and that means that our notional kilogram of additional weight is going to cost us around 0.305 * $1.45 = 44 cents per Kg of cargo weight. That sounds like a steal! So adding a Kg. of battery will cost somewhere within an order of magnitude of $0.50 per flight.

How much does the battery weigh? Hm. Teledyne Benthos, one manufacturer of pingers for flight data recorders, states that the beacon itself weighs a maximum of 190 grams. That's not a lot! Let's say that 100 grams of that is battery weight. So one tenth of a kilogram. Doubling the battery would add 0.1 kg, or 5 cents per flight. Again, not a lot! We'll totally punt the cost of the bigger unit. The ELP-362D seems to cost approximately $3,000.00 US. The batteries last 7 years, so figure it costs approximately $150/year for the battery. Even if we double that, we're looking at $0.50/day for the battery - which is an order of magnitude more expensive than the fuel cost of doubling the battery via straight mass increase.

I have to be honest, I hadn't realized how negligible that cost difference would be. Okay, that doesn't seem like much of a barrier. But again, multiply it out. We're talking $0.50/day for every aircraft in the fleet for these bigger batteries. How many are there? Uh, well, American Airlines, the world's biggest, appears to have around 1500 jetliners. So we're talking $750/day for this increased battery capacity across the fleet. Now, how many airliners are lost where this capacity makes a difference? Realistically, in the past few years, there have been *two* - Air France 447 and Malaysian MH370. Air France is actually not necessarily countable, because the aircraft was found two years later - because good position data was available on where it was lost, and they found wreckage to confirm that data, rather than finding the black box beacon. So really, in the past 30 years, if you take only those crashes where the FDR was lost at sea and not located presumably due to the beacon malfunctioning or not lasting long enough, you get...really, two. AF 447 and MH 370. All the others were situations where the location of the crash was known but other circumstances prevented finding the FDR (in some cases, the aircraft were destroyed by explosion, and the FDR likely didn't function).

So let's say 15 years in between incidents where this would be relevant. 15 years, at $750/day for American Airlines alone, and you get $4,106,250. For one airline. That's quite a bit of money. Just for the heck of it, add in the $0.05/flight for the increased weight, and end up with $150/day assuming two flights per day per aircraft. So another million, nearly. The top ten airlines by fleet size have approximately 7,000 aircraft among them. This probably is less than half the total fleet size.

A third option - we could modify the FDRs to ping at intervals, conserving their battery. Let's say we had them broadcast 50% of the time (or increased the interval between pings by 100%). Let's ignore the problems that would cause in having to have slower search patterns, and assume that's not an issue. That might improve things. But the signal pulses are already roughly 1 per second. Much longer, and noise makes it harder to identify them. But it's probably still the best option.

Note, this completely punts the costs of redesigning the units, of testing and certifying them, and of the cost to replace the current fleet equipment.

UPDATE: At least one standard ELP, the Teledyne Benthos I reference above, in fact has a 90-day battery option, and doesn't mention any difference in weight. This leads me to believe that the difference is purely in cost. There may be aircraft out there with 90-day battery FDR ELPs right now. The minimum required is 30 days, I believe.

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