Each privilege has a price - Accident Report 1by Charlie Marais
ACCIDENT REPORT OF ZS-SAR - CESSNA 152
27 APRIL 2013
The aircraft, a Cessna 152 with registration number ZS-SAR, was hired by a member of the Worcester Flying Club for a local private flight. The pilot had indicated to the flying club members that he intended to fly for approximately one hour. The aircraft took off from runway 33 at Worcester aerodrome (FAWC) at approximately 1420Z. When the aircraft was overdue for landing by approximately one hour, the club members began to show concern. They phoned the pilot on his cell phone, but without any response. They then started phoning farmers in the area, as well as air traffic control (ATC) at Cape Town International aerodrome (FACT) to enquire whether the aircraft had been in radio communication with them, which was not the case. At around 1900Z that evening they received a call that the wreckage of the missing aircraft had been located on the farm Wittekop, which was located 9.2 nautical miles (nm) south east of FAWC. The pilot was fatally injured in the accident.
The right-hand rudder cable was found to have failed. This most probably rendered the pilot without rudder authority to counteract the spin and recover from the manoeuvre.
COMMENTS BY CHARLIE MARAIS
Call it speculation, fishing, guessing or whatever you want; the fact is that we actually do not know what happened that day. However, having said that, there is no need for us to abandon our attempts at finding out what happened or to be more accurate, to find out what probably or most probably happened. The reason why we have to look at all possibilities is not to apportion blame, but to ensure that we are prepared for any possible eventuality that could lead to a situation developing in the future. The pure postulation of scenarios therefore is only to learn from and not to factually stipulate what had happened.
The recent top ten list of accident causations as released by the FAA is listed as follows from number ten to number one: 10 - Weather (wind shear or thunderstorms), 9 - Mid-air collisions, 8 - System component failure (air data sensors, suction pumps or gauges), 7 - Fuel related (fuel contamination, fuel starvation), 6 - Other (procedural errors, track and altitude errors), 5 - Unknown (no definite clue to causation), 4 - Low altitude operations, 3 - Engine system component failure, 2 - Controlled Flight Into Terrain and 1 - Loss of control. Note that the case of "not knowing" is quite high up and weighed in at number 5 and "loss of control" is the top scoring accident causation element. Well, in the case of this particular accident, we are actually aware of a few facts and this, as well as the "unknowns", will form the basis of the discussion.
In accident investigation we always start with the hole in the ground and work our way backwards. In this case we firstly know that the aircraft impacted the ground with very low forward speed, a very high rate of descent and a continual yaw about the normal axis to the left. This leads to the conclusion that the aircraft was in an incipient spin prior to impact. I say an incipient spin, as it takes up to six turns for the aircraft to settle into a fully established erect spin. For this argument I will use the term spin to replicate the type of manoeuvre the aircraft was in prior to impact. Preceding the actual spin, we know from the witness that the aircraft was first flying straight and level, and then initiated a turn to the left which then showed a nose up attitude change and the aircraft entering into a spin. What we do not know is why the aircraft ended up in a spin. This will have to be discussed. What we also need to acknowledge is that the right rudder cable snapped due to excessive wear and that it failed due to tensile pressure (it was exposed to forces greater than it could handle, hence a stretch and break). The possibility of the cable snapping at straight and level is minimal and therefore not considered as a factor in entering the stall or spin condition. Inductive reasoning and laboratory testing leads us to the most probable time when the cable broke, to be when recovery action for the incipient spin was initiated. As it was the starboard cable and the spin was to the left, the reaction most probably was a hard right rudder input from the pilot that lead to the cable snapping. Note that the condition of the cable was definitely outside specifications and thus in no way the pilot's doing. It does not matter how hard he pushed the right rudder, a serviceable cable would not have snapped. The snapping of the cable during the recovery attempt is therefore the most probable time that the cable snapped.
While I am on the topic of the cable, this specific rudder cable is made up of seven strands. Each of the strands is made up of 19 carbon steel wires. The seven strands make up the cable and all strands are exposed to outer friction, except for the centre strand. All the wires, except those in the centre strand, were worn to less than 50% of the original diameter. Six of the strands failed due to excessive wear and the core strand failed due to tensile fracturing or stretching beyond capability. The wear should have been picked up by the AMO during the annual inspections. Pilots simply cannot do a pre-flight being attentive to the parts of the aircraft and engine that cannot be observed. When a cable shows fraying, the AMO will immediately replace that cable without a second thought. To pick up a cable that has no strands or individual wires being broken, or frayed, as being outside specifications takes a keen eye and not a general glimpse. In this case there was no fraying, just a very noticeable flattening of the individual wires from the outer strands where it made contact with the cable pulleys. The aircraft flew 9700 hours since arriving in SA with no cable replacements.
This then leaves the question of why the alleged spin was entered. Yes, alleged, as there is no evidence that he actually wanted to spin and I will reason this in the statements to follow. Although not proven, the height of the aircraft prior to the entry into the manoeuvre was far below what any reasonable man would attempt to spin from. Even if the height was another 500 to 1000 feet higher than the estimated 1000 feet, this would still not be the ideal height to enter a spin from. The accident analyses showed that a book with three highlighted chapters was found in the cockpit and it is strongly suspected that the book was on the front seat next to the pilot. This leads us to the belief that the pilot wanted to practice forced landings, precautionary landings and spinning. The aircraft was believed to have been airborne for only 15 minutes when the accident occurred. Yet another of those items that does not make sense. The reasonable pilot would keep the more difficult exercises until later in the sortie when confidence was gained, or if lost, not try it at all. I also have not heard of a "low time pilot" such as this one, or a PPL for that matter, that would willingly and knowingly try spinning on their own. The average PPL does not even want to practice stalling on their own, never mind spinning. No, I certainly do not buy that this pilot had spinning in mind. Perhaps he had a precautionary landing planned, but besides that nothing strange or remotely dangerous.
Let us consider his hours for now. He completed his PPL in 18 consecutive days over the December holidays in 1999/2000, having accumulated 54.9 hours post initial test. This was quite possible before the PPL online examinations slowed the pace down. He ended up with a total of 173 hours, which over the period of time meant he flew on average 45 minutes per month. My deduction from this is that only a super arrogant man would fly that seldom, in his case only 2.5 hours in the last 90 days of which 0.5 on type, and then try a low level entry into a stall. There is absolutely nothing to suggest that this pilot was arrogant. He actually read up on forced landings, precautionary landings and spin manoeuvres. He flew a little, but there is no indication that he tried any "funnies" outside of his zone of comfort or experience.
The question now remaining is what was he busy doing and what lead to the inadvertent entry into a stall, where the wing dropped, he tried to recover, but because of the broken cable and low height left, impacted the ground? What would make a wing drop? Naturally it would drop if that wing stalled, either during straight and level, or during a manoeuvre. Any flight condition other than straight and level is referred to as manoeuvring, therefore the basic stalling speed is always when an aircraft with engine or engines throttled back, can no longer maintain straight and level flight. When turning, climbing or descending, or a combination of the above, we then have to use the manoeuvre stalling speed. This simply means that if the "g" that you are exposed to, or more accurately, the load factor, is higher or lower than 1, then the stalling speed will either increase (positive above one "g") or decrease (negative "g" or less than one "g"). The aircraft was in a turn to the left when the nose pitched up, more positive "g", thus higher stalling speed, when the left wing drop occurred. I could not determine how long he was in the turn before the wing dropped in the climb, but the climb combined with the turn would have decreased the indicated airspeed. The wind on the other hand was a factor not really paid attention to as the weather was fine. But the wind was around 260°/12kt, gusting 23kt. The turn commenced with the wind from the left and at some stage the aircraft would have been exposed to a cross and then a tail wind. A wind of 23kt in a low speed turn, when the aircraft turns rather quickly, could easily have been a major factor in the wing drop, or the aggravation of the wing drop. Level low speed turns in gusting wind conditions have taken many lives in the past. At that height he only needed to pay less attention to the height, as would be expected of such a "low time" and "low recency" pilot. Show me a pilot who flies less than one hour per month and I will show you a pilot that cannot properly maintain height, heading and speed, let alone maintain these parameters under manoeuvring and wind gusting conditions, especially in a slow and rather underpowered aircraft.
This is not the only question that is unanswered. What about the power? The throttle was found fully open, but the prop showed one blade tip bent forward and the other had no damage due to rotational impact. A prop bent rearwards means no power on the prop. Full power on the prop would have shown the tip bent forward as the prop wants to bite into the ground. There was no biting, thus no power. They could find no problems with the engine, and as such for all intents and purposes ignored the open throttle, suggesting that during a prolonged spin the engine could cut. Well, I suppose this is the easy way out answer as anything is actually possible and as such we can skip most arguments. I have done far in excess of 1000 spins in my life; most of those with three to four fully established turns. In some cases we had as many as 11 turns and then there was a test where we spun 14 times. Not once have I experienced an engine cut, or the slightest suggestion of one. Maybe the Cessna 152 engine just does that? Unfortunately there is no evidence to prove this theory; in fact, experience suggests otherwise.
Let us put ourselves into the pilot's shoes for a moment… So, I am in a turn to the left, the engine cuts on me and I do the first thing that I was taught, namely to put speed into height. I overdid the pitch-up due to my initial panic and then the wing dropped with the gusting wind not being favourable. I do what I was taught and remotely remembered from my last test, and I also read about it in the book lying next to me, so I put in opposite rudder to stop the "C" gyro. In my panic I was rather harsh on the rudder input and to my utter dismay, the right rudder went slack. The ground is rushing up and seeing that there are no way out, I did what instinct requires and I pulled back on the yoke to get away from certain death. It all happened so quickly and I never felt the impact with the ground.
Yes, I fully believe that the pilot did not want to spin or stall, I believe that the wing drop due to stalling was inadvertent and that due to the high wind gust conditions, the left wing dropped quickly and he tried to recover. The cable snapped and he was too low to try anything else. In fact, he was probably too inexperienced to have known about anything else that he could do. The engine was not working and we would never know when it actually did quit on the pilot, but I believe that it was a very probable scenario that this happened during the initial part of turning.
Note that in the top ten accident causations, we have an element of "unknown", but then a "loss of control scenario".
Less than one hour of flying per month and only due for a check or test every 24 months is a sure recipe for disaster. Please do not stop flying, but how about taking along that dreaded instructor to brush you up every six months? Is your life really that cheap? I know it is your decision, but it is our loss.
Reading up on emergency exercises is good. To get a competent person, which must be an instructor, to patter and sharpen you up, is good airmanship and shows great consideration towards your loved ones and therefore is far better.
Ignorance is bliss. That which you are not aware of will not bother you and will always catch you by surprise. Choose an AMO that will not leave your rib cage open to surprises. You must become more aware of the maintenance of the air vehicle. What do you know about engine care, or airframe maintenance and avionics calibration? I write these inputs to get your attention focused on such hidden, yet potentially devastating items, such as cables. Oh yes, I have heard many times before that the AMO says that they should replace an item and you think that they are just out to make money and the agreement is; "Next time". Fraud said that we all think we are immortal as we always keep on postponing things to later or tomorrow, but tomorrow is not a guarantee and neither is mechanical sub-standard maintenance. When there is doubt, there is no doubt. Yes, we all know this one, but few actually walk the talk.
An enquiry into an accident must never take anything for granted nor consider something of lesser importance without full argument and logical explanation. The human, and as such our reasonable man behaviour, must always have a part in actions or non-actions.
There is a general lack of aerodynamic understanding amongst our PPL and even CPL pilots. Aerodynamics is not just there to make examinations difficult; they are there to ensure understanding. Understanding is fundamental in decision making - decisions on when to do something and when to do nothing, especially if you are more rusty than air-worthy.
The majority of people dream to be a pilot. A very selected and privileged minority get this privilege. Each privilege has a price, but it need not be your life.