In the course of a few days, two old piston twins, a Model B55 Baron and a Piper Navajo, crashed, killing six in each case. There was a family of three, a friend, and two pilots in the Baron. They were going to a graduation. Professional folks, three couples, returning from a meeting were lost in the Navajo. Terrible tragedies.
The NTSB will be a while getting out probable causes so what I am going to share here comes mostly from newspapers and TV accounts as well as from NTSB preliminary information and some basic research. I am doing this to see what, if anything, has changed since I wrote an article entitled Double Trouble (what else?) on the same subject in AIR FACTS over 50 years ago. I’ll tell you in advance that while some things never change, others do. My main question about the recent accidents was whether or not they were related to the failure of one engine and the resulting asymmetric thrust.
The Baron was landing on a 2,999 foot long runway, it touched down about midfield, bounced some, and then the pilot apparently thought things were not going well so he aborted the landing, staggered into a go-around, lost control and crashed.
The first thing that came to mind was the center of gravity. In a basic Baron with six on board (three were teens but from the pictures they were grown) to keep the center of gravity in limits there has to be some weight in the nose baggage compartment. This was likely there, but the cg could have been close to the aft limit which means the airplane would have been none too stable in pitch.
A brief solo hop got the airplane together with another pilot and the five passengers. There was some discussion there about the fuel load which was apparently limited some because of the cabin load. The departure and flight appeared to have been routine.
A balked landing can be a whole ‘nother matter, though, especially when using a runway that is none too long for the airplane. There are trim changes, configuration changes and performance challenges. Couple that with the sudden stall characteristics of airplanes of that vintage, especially twins, and events can come to an unfortunate conclusion.
Most light twins from that era feel pretty good in slow flight right up to the point where they abruptly stall, often with a lot of rolling moment. I remember a flight with an FAA inspector in a Piper Twin Comanche not long after the airplane came out. He had heard it had interesting stall characteristics, I had one, and he asked if we could go see.
See we did and I can only say that we both agreed on the control inputs required for a recovery from inverted flight because we were both on the controls, both doing the same thing. Neither he nor I ever again flew a Twin Comanche well into a stall.
So nothing has changed over time. The aging fleet of twins is just as unforgiving of a pilot getting too slow too low as it ever was.
According to the NTSB preliminary report, the Navajo pilot reported that he had lost a fuel pump and wanted to divert to a nearby airport. En route to that airport, the pilot reported that he had lost the other fuel pump. I would presume that when he reported a lost fuel pump, it meant the engine had failed. After that the airplane descended steadily until it hit trees 1,650 feet short of the runway. Nothing in the report gave much hint about whether or not the pilot lost control of the aircraft but the condition of the wreckage suggests that as a possibility.
I have written about similar crashes involving one failed engine. The pilot usually starts the engine-out arrival with an abundance of stored energy, altitude and airspeed, and as the approach unfolds that energy is not used properly. The airplane winds up too low on approach and, with the added kicker of asymmetric thrust, the pilot gives away too much airspeed and one of those abrupt stalls I mentioned a moment ago occurs.
In this case asymmetric thrust does not seem to have been a factor and when the final report is issued there will likely be word on why both engines apparently failed. I can think of only one logical reason. Whatever the reason, there is not likely to be a lot new about this accident. It could have happened recently or at any time in the past 50 or so years.
There is no question that pilot skill plays a larger role in light twin accidents than it does in single-engine retractable accidents, for example. I think a go-around in a Bonanza is less demanding than one in a Baron and a single-engine or dead stick landing in a Piper Malibu should be easier than one in a Navajo. An engine-out landing should be easier in a Navajo but, unfortunately, that does not always seem to be the case.
It has often been said that a pilot buys a light twin and flies it successfully until one engine quits, then boom.
One thing that changed a bit over time with twins is the relationship between asymmetric thrust and accidents
Fifty years ago about 20-percent of the fatal accidents in light twins were related to the fact that the airplane had two engines and was attempting flight using but one of those engines. More than half those accidents happened during instructional flight. Recently almost half the twin accidents were related to asymmetric thrust and almost half those were in training. The sample today is much smaller and thus less meaningful.
There was a logical reason for so many training accidents years ago. The FAA required that Vmc (single-engine minimum control speed) demonstrations be done as low as possible but not below 500 feet a.g.l. Vmc is usually close to the stall. So here is the airplane perilously close to the stall at 500 feet when the power on one engine is retarded. It takes little imagination to see what might come next.
The first accident related to this policy came during a check ride being conducted in a Beech Travel Air by an FAA inspector. I knew three of the four people killed (two were observers) and one was a close friend. The date was July 22, 1958, which also happens to be the date I went to work for AIR FACTS.
Many more such accidents followed, usually in Beech Travel Airs and Barons and Piper Twin Comanches. If the trouble started high enough, the airplanes would come to the ground in a fully-developed flat spin. The Army lost one of its most experienced T-42 (Baron B55) instructors in a flat spin that I heard started at 5,000 feet a.g.l.
It took years but the FAA was finally convinced that its procedures led to awarding the rating to the survivors of multiengine training. The Vmc demonstration and training requirements changed pretty dramatically.
Two other things that helped with the training problem have been the Beech Duchess and Piper Seminole light twins. These airplanes are much more mannerly at the stall and Beech actually did full spin tests on the Duchess, including spins with one engine wide open and the other shut down, and it was always recoverable.
There are few flat spin accidents in light twins today, mainly because the airplanes that were prone to that are no longer used as trainers.
When teaching multiengine students, I insisted on landings with one engine secured, prop feathered and all that. This was controversial because some thought it involved too much risk. My justification was that I did not think multiengine pilots should be put into the position of having to do something (an actual engine out landing) for the first time with passengers on board.
The airlines were able to take the risk out of engine-out training with simulators. Unfortunately that can’t quite be fully accomplished in piston twins though some of the training aids available now come pretty close.
Plenty of attention was always placed on the vaunted engine failure on or soon after takeoff. All that training and practice was aimed at maybe two minutes of each flight. Most light twins will, in two minutes, get off the ground and up to, say, 1,000 feet in that length of time. Once there, and regardless of where and when the failure occurs, the challenge becomes getting the airplane safely back on the ground.
Getting back down might not seem like much of a challenge. Apparently the FAA doesn’t think it is because in the official publication Flying Light Twins Safely there are only two short paragraphs about engine-out arrivals. Trouble is, there have always been more fatal crashes during engine out arrivals than after mechanical failures of engines at a critical time on takeoff.
I always liked to teach that there is a critical altitude above the ground when considering any engine out scenario. The altitude is the same for a departure or arrival and depends on how sharp the pilot is. It might be a couple of hundred feet for the ace of the base and a thousand for a lesser pilot.
On takeoff, this is the altitude from which you would have good options if an engine failed. On arrival it is the altitude below which you are totally committed to a landing, no go-round allowed.
Quite a while back (40 years ago) there was an actual Baron 58 engine failure at the worst possible time on a night takeoff from a normal-sized general aviation airport. A prominent politician and his family were lost so there was extensive discussion about the accident.
It was determined that the crankshaft broke and the engine abruptly lost power at or right after liftoff. The pilot apparently failed to retract the landing gear but he did attempt to continue and subsequently lost control and crashed.
If I recall, it was determined that, all things considered, if the pilot had done everything perfectly, it might have been possible to maintain control, climb slowly away, and fly to a successful landing. I have forgotten whether or not they addressed this but the pilot could also have aborted the takeoff and avoided the out–of-control crash that killed Congressman Litton and his family.
What I took away from all that discussion is that few pilots could master the burst of brilliance and fancy footwork required to handle an engine failure and continue successfully given those circumstances.
I’m talking about legacy airplanes here. Most consider that to mean those built before the drastic contraction of light airplane manufacturing in the early 1980s. Most of the airplanes considered are over 35 years old, many are as old as 60. I mention this because some of you might wonder about the Cirrus and Diamond airplanes in relation to the discussion. Simple. They weren’t born yet so are not considered here.
It was always interesting to compare the piston twin and single-engine retractable accident picture. The airplanes were and are used for similar missions, mainly transportation, and are usually flown by pilots of similar training and capability. A lot of pilots thought they were buying safety with a twin and the numbers often showed that not to be true. Some of the retractable singles had lower accident rates than similar twins.
I looked at the relationship between accidents in these two groups of airplanes and IFR activity and nothing has changed much over the years. They are in the IFR system and are involved in fatal accidents in about the same ratios now as 40 years ago.
I did come up with one raw number that was quite surprising. I knew that both fleets are smaller, because of a lot of low production years as well as a lot of attrition. I also knew that the individual twins fly less now than then, mainly because of maintenance costs and the perceived need for payday loans at the gas pump. I also knew that this meant there would be substantially fewer wrecks today because hour-based accident rates have not changed all that much.
I had no idea how many less until I compared 01/01/2016 – 08/16/2016 with 01/01/1976 – 08/16/1976. You ready for this? 2016 – 12, 1976 – 70. Yikes. You can hardly look at that number and conclude that piston twins are having more trouble now than then.
My interest in this post was prompted by current events. It turned into a history lesson because it is becoming ever more apparent that the piston twin is slowly but surely joining the brigantine in the history of human transportation. Too bad because they sure were fun to fly.