The problem of jump-starting your plane is you have no idea of the condition of the battery once it starts, and it will be at least 90 minutes cruise or possibly not at all before the battery has any true backup value. A strong case can be made that you are operating an un-airworthy airplane, particularly if you have a modern plane and flat screen of integrated avionics.
What makes this even more dangerous is the new demands of flat screen avionics, which have terrific current demands at all times and a limited ability to reduce the current load on the battery(s) while you try to get back on the ground.
It’s the potential danger of flying after jump-starting an installed battery of unknown reserve capacity or knowing if it’s still airworthy. It should be tested and charged before any flying takes place if you are a responsible pilot. Chances are strong that there are two batteries, both of marginal capacity, as this concept of dual batteries evolves into being one that is safe, not more dangerous than an old fashioned system than can be shut down piecemeal.
The DA-42 Incident and Computers
In this case, the results of jump-starting had consequences far out of anyone’s wildest imagination. The aircraft was a brand-new Diamond DA-42 twin with turbo-diesel engines and full FADEC controls i.e. the computer controls everything. Apparently, it can even command full feathering of the props and engine shutdown without pilot input.
According to the report, the new airplane had a dead starting battery and a simple jump-start was requested and received for both engines (contrary to the POH). Shortly after takeoff on March 4, 2007, from a German airport, at gear retraction the airplane experienced a FADEC/electrical control unit commanded dual engine shutdown as well as prop feathering at low altitude. The Diamond twin pilot had to make a very quick emergency landing, resulting in a crash to the side of the runway.
The nearly dead primary battery, (there is only one primary system battery in this plane and small backup battery) with the addition of the gear motor load, apparently did not have sufficient power reserve to operate the FADEC/ECU system, so the ECU shut down both engines and feathered both props, which is how the system was then set up. And factory installed secondary batteries to support demanding flat panel systems is becoming standard for newer aircraft. We are finding batteries of marginal capacity under the best of conditions. Sort of seems like a step back in electrical safety.
The Diamond primary aircraft battery is quite small in capacity at 24 volts, 10 ah. There are two dedicated alternator excitation batteries of 12 volts, 1.3 ah each wired in series, but they only have that single function—backup alternator excitation.
In our opinion, there may be an aircraft system problem here that needs to be addressed beyond simple warnings, which may or may not have yet been addressed since this happened. It is no longer limited to Diamond. New Cessnas and Beech and Pipers and more have secondary batteries of questionable capacity to keep the flat screens running should the alternator fail or the primary battery fail. It is far more complex than it used to be of simply shedding loads.
The DA-42 electronics system is quite different in the way the redundancy of the dual bus works on, say, the Columbia aircraft, which has an independent dual electrical bus and two system batteries. The DA-42, on the other hand, depends on a single primary battery for all but emergency alternator excitation.
The fact that engines in the DA-42 shut down when the primary battery fails under certain circumstances we find disconcerting, but the FADEC controlled diesel engines depend on outside electrical power to run. (A magneto-equipped engine, once started, will run regardless of the battery or alternator condition—as long as a gear-driven alternator has not trashed the engine.
Can it be that the old-fashioned single battery, simple, unconnected analog or basic, digital avionics are safer than interconnected avionics with dual, but marginally sized, dual batteries? There is obviously a learning curve for the makers with extra batteries and alternators to do their jobs right as well as the pilot. These new fancy avionics are not your father’s simple avionics stack. For example, a self-exciting alternator is a huge advantage if you have a bad battery. Why are they not all this way?
Batteries in good condition are more important than ever for fancy new flat panel systems, and another reason Part 23 airplanes need scheduled capacity checks of both batteries.
Just how much authority should a FADEC system have to rule the airplane? Granted, the pilot did not follow the start sequence to the letter, but the consequences were extreme. In our view capacity checks of these systems is clearly a mandatory function, not voluntary.
This accident information was preliminary, and could contain some errors in assertions, but the basics have been confirmed through several European reports on the accident as well as a reprint in Pilot und Flugzeug Magazine on the accident. (A Google translation from the more detailed German article was used to read and compare the article to the English version.) Diamond also sent us electrical system schematics of the circuit.
So far, we have seen an SAIB (informational only, CE-07-38). There is a European safety bulletin (EASA) on DA-42 starting procedures dated in April 07. Diamond has also published a safety bulletin: SI 42-040. (Only one engine is supposed to be jump-started; the other is to use the aircraft battery itself to start the second engine.)
In our opinion, the electrical system should be designed to be more forgiving of minor excursions from the approved starting procedure. The system is using so much computer power that it should have a fail safe built in to not allow an engine to be started with deficient batteries because a pilot is not properly versed in their plane’s capabilities. (Since this article was written, the design was revised as described at the end of the article. Ed.)
A warning alone does not seem adequate for such a modern, high-end design. Further, the fact that a previously jump-started battery will start a second engine is not necessarily proof of a dependable battery or truly redundant system, quite the reverse seems to be the case.
Diamond has informed us that there will be an AD that adds another battery to the mix. This one will be designed to specifically back up the ECU—a great idea for safety, and it’s to Diamond’s credit for doing so.
But we would recommend that Diamond consider adding a second primary battery (or al least a significantly bigger one) considering this is an all-electric airplane. But all this is a lead-in to the premise of this article, that jump-starting is a practice that should be strongly discouraged for all aircraft, period, because you do not know the status of the primary battery.
Risky Business
This accident showcases the risk of jump-starting any aircraft with a dead battery. If you are planning to stay local or in the pattern, as opposed to starting off cross-country, you reduce, but don’t eliminate the risk of a bad outcome from an electrical failure. With an all-electric airplane, you are probably in an even more risky situation.
We know there are planes without electrical systems, but we are talking here of safety and utility in populated radio mandatory areas, not VFR, severe-clear puddle-jumping with no radio from a grass strip. (Which is not to say that is not fantastic fun in its own right.) Also, we stuck with the original model designation of Part 23 aircraft, which may have newer improvements, so you can compare to the latest versions.
When you simply jump-start, you don’t know why the battery is dead, nor do you have any idea that it will charge back up properly. Moreover, even if it does charge back up it will take hours, not minutes before you have a legally airworthy battery that has the required emergency capacity available if the battery is OK. And with all-electric airplanes, the need to adhere to the manufacturer’s ICA requirement for annual battery capacity checks is more important than ever. We have one direct experience of a Piper Cherokee Six on air taxi work that took of with a jump start. That progressed into an emergency with a fried alternator 100 miles from home. Expenses were all out of proportion to the dead battery problem—as well as a probable lost customer.
Why Have Power Plugs?
One can legitimately ask if jump-starting is so dangerous, why are there external power “jumper plugs” built into many aircraft? Actually, it’s an extra cost item in many models, and for many uses, such as for maintenance purposes as well as an external plug-in for those situations where the owner wants to work on proficiency without draining the battery system. They are also convenient for recharging the battery, especially if the battery is in some inconvenient spot (when the maintenance manual allows this—not all do).
There are also special, plug-in devices that can act as ground power units. Sportys sells such units for around $400. It’s a great way to practice and learn your full suite of avionics without draining the battery—particularly helpful with the all-electric, modern, multi-function displays. It also provides the power reserve recommended for a proper gear retraction test.
And of course the external power receptacles provide an emergency means of starting an aircraft when there is no other way. Just remember, the use of the power plug should not be a substitute for a bum battery.
It’s just a matter of time before something goes wrong, if you use jump starting as an excuse for poor or deferred battery or charging system maintenance. To jump start prior to IFR, night or even cross-country flight can only be construed as plain foolhardy.
I don’t think most owners understand the time involved to recharge a battery that is also serving as the aircraft system battery at the same time. Don’t forget the battery is also supplying system power while charging back up.
Moreover, a full battery acts as a big electrical buffer and reservoir to help protect the avionics from system spikes and surges and provides reserve power for operating big loads such as the landing gear (even hydraulic gear). When the battery is dead or very low, this reserve amperage capability is lost.
Here’s what the Columbia 400 maintenance manual says on jump-starting: “Never “jump-start” an aircraft that has a “dead” or discharged battery. It takes approximately three hours to recharge a fully discharged battery with the aircraft generating system or external power.”
Learn Your Systems
You need to know exactly how your electrical system works if there is a power emergency, especially if you have an all-electrical panel of power-hungry avionics. The new dual battery, all electronic systems are quite complex—and apparently not all the bugs have been worked out of some systems.
If you own or rent an all-electric airplane there is no reason to let down your guard for system backups. You need to thoroughly understand the new dual bus systems and where the redundancies are, as well as how to quickly configure your plane for optimal i.e. minimal power consumption.
Powering those gorgeous panels takes lots of juice. Handheld transceivers and a handheld GPS are still important things to have in your flight bag—possibly even two backups. Even if you have dual batteries and dual alternators, there is no guarantee the second battery or alternator will provide long usefulness as they are minimalist for light weight. And not all designs are the same—you should make it a point to know exactly what the capacities are of your system, so if there is a partial failure you will know what loads to shed and how to do it quickly, and options of what to do first.
And of course, all-electric panels need even greater attention to maintaining the battery(s) in top condition. The second alternator in a dual alternator system for a single engine aircraft may or may not be a lower capacity unit. In the Columbia 400 there are two 60-amp alternators.
As a contrast, the Cirrus SR-22 has a 60 amp primary alternator and a 20 amp secondary alternator. The primary and secondary battery configurations are also different capacities in the Cirrus.
You will need to be aware of what power use configurations will not overload your second alternator if the primary alternator goes off line. This means doing your homework in understanding the details of the POH.
In the Columbia 400, for example, switching bus systems to cover failures is controlled by cross-tie switches on the panel or overhead, so it’s important to know how the system works and what is connected to each electrical bus.
Also, in the Columbia 400 there is a special switch for bypassing the power grid and connecting the No 1 Nav and Com and GPS directly to the right side battery. Cirrus uses a very different, somewhat automatic system for the backup alternator to power the main bus in the event of a primary alternator failure.
It is ironic that the new dual electronic everything systems in modern singles have far from eliminated the need for careful emergency power loss planning. It’s just now, instead of back-up vacuum systems, it’s back up batteries and second and even third alternators. (These systems are power hungry—there is a third alternator option in the Columbia 400.)
Self-Excitement
A very interesting safety feature of the Cirrus SR-22 with dual batteries and dual alternators is that it has self-exciting alternators. Once started with battery power, they no longer need to continue to be provided with a field excitation current from the battery. This is a rare electrical safety feature all aircraft alternators should have, but especially all-electric airplanes.
If the batteries fail the alternators will keep on charging in the Cirrus with self-exciting alternators. Nevertheless, without battery power, heavy system loads may cause malfunctions or erratic operation without a battery to supply reserve capacity, so loss of battery power is still an urgent situation. The battery is a huge filter and reservoir of power.
Additionally, we have seen on the various forums on the Net where the batteries on some earlier all-electric models of these dual alternator, dual battery systems need replacement every six months. Whether it’s a heat issue or an overcharging/undercharging issue or if the batteries are not up to snuff or undersized for the task, we don’t know at this point. We will be watching and solicit user comments.
It just seems that sometimes progress is elusive. Don’t let an all-electric aircraft lull you into complacency. These new aircraft are fantastic, but they can be demanding.
These new flat panel systems are all different and it is up to the pilot to become familiar with any variations they will be flying, as some of these design changes are significant. It’s too bad there is so much change in backup avionics systems. Of course that’s not what you see when you look at the panel or what sells the plane for most buyers.
Truly a great deal more will be expected of pilots to know how to operate the latest generation of flat panel aircraft in an emergency mode as there are many varieties of FAR Part 23 implementation, some much more pilot friendly than others. You can thank Part 23 for the requirements, but thank the makers for how complex, redundant, and effective the manufacturers make the systems.
We sure have not seen any great strides in simplicity in the recent years of flat panels as the manufacturers have had adequate time to integrate systems. We would like to see more redundancy as a trade-off for bells and whistles. We are much bigger fans of redundancy.
Consistently Inconsistent
One but has to briefly review the many different ways dual batteries and dual alternators are set up to quickly come to the conclusion that while the basic simplicity of CAR 3 certified aircraft, notwithstanding those owners who invested small fortunes in older aircraft via the STC or even the field approval route.
For these owners an extremely thorough examination of the planing that went into the electrical integration of old and new systems, whether dual electrical backups were included as part of the installation and any that went into the system design to make an old-fashioned airplane suitable for 21st century IFR.
Poorly designed redundancy can end up having the reverse effect of making the aircraft harder to use than an old King KX 155, KI 214 and a basic IFR certified GPS unit, which is a very different animal than a pair of huge, flat panel displays that use power and run the entire panel. Retrofitting systems is much more difficult than a factory designed system from the circuit breakers on up. Think about that before you think about retrofitting.
Secondly, spend a lot of time understanding and comparing exactly what options you have when an electrical failure occurs.
Is This Progress?
The airplane and avionics makers have had the opportunity to standardize the design and functionality of installed flat panel systems over the past several years. Instead the time appears to have been used to try to one-up each other in multi-functionality rather than improve critical but less visible, redundancy, and ease of response to a system failure situation.
Dramatic system differences still exist, whether from dual battery power or a dual, self-exciting powerful alternator, or other ease of system backup.
These systems have shown themselves may not be as easy to use as we would like to see. You could find a confused airplane system in an electrical emergency when compared to an old CAR 3 style plane with simpler sources of power distribution. It’s sort of the aviation version of keeping it simple. That said, be sure to have a hand-held nav and com or other backup device for an alternative.
Unfortunately, new designs take time to get backup systems both robust and simple to use. We left the model references as they were in the original article a few years ago for that reason. If we were buying a new plane today we would like to see if any shortcomings have been addressed or other problem areas surfaced.•
This article originally appeared in the March 2014 issue of Light Plane Maintenance magazine.
Since this article was written, significant changes have been made to the DA-42 electrical system that prevent the problem that lead to the accident described. We received the following from Peter Maurer, President of Diamond Aircraft:
“The accident DA42 aircraft described in the article was equipped with only a primary battery and no FADEC ECU backup batteries. As the article states correctly, the accident happened primarily as a result of the pilot jump starting both engines with a known dead battery, against POH recommendations. Notwithstanding this primary cause, once it was recognized that the TAE FADEC did not tolerate voltage drops well and that such voltage drops could result in a FADEC reset and subsequent engine failure, the airworthiness authorities imposed airworthiness action to revise the TAE installation instructions to highlight this issue, such that installers (e.g. OEM’s) ensured that stable voltage was available to the FADEC under foreseeable conditions. At the same time DAI revised the design of the DA42 electrical system to include the FADEC backup batteries that every diesel engine powered Diamond (both TAE and Austro) is equipped with, to provide stable and constant voltage to the FADEC, even if both alternators have stopped generating. The backup batteries supply only the FADEC ECU when needed and even with a completely discharged primary ship battery, the engines will continue to run till the fuel runs out, if at least one alternator is also operating.
“The bottom line is that the DA42 has many layers of electrical redundancy:
- Primary Battery
- Dual Alternators, each powered by the respective engine
- FADEC ECU backup battery per engine (this is only needed to provide excitation to the alternators and to bridge any transient voltage drops in case of abnormal electrical system operation. If the engines are running and alternators operating, power is not drawn from the ECU backup batteries. The only case where ECU backup batteries would drain, would be if the primary battery was discharged and both alternators had failed.
- Backup batteries for standby instrumentation
- It should be noted that the system layout allows “cross-feeding” of the alternators and ECU backup batteries.
- No pilot action is required re operation of the ECU backup batteries and their replacement, when required, is easy and low cost (maintenance free lead acid).
“There are no cases of electrical system caused ECU failures known to us, since the incorporation of the ECU backup batteries.
“It should also be noted that both the AUSTRO ECU, as well as the later TAE (now CM) ECU’s, are less susceptible to transient voltage fluctuations than the ECU configuration of the accident aircraft.”
AVweb thanks Mr. Maurer and Diamond Aircraft for the update.
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