Especially when you’re two miles out at sea.
Picture this: An R22 helicopter without floats operating two miles off the coast of Miami, FL. On board is the CFI-rated pilot with
600 hours of total flight time and the private pilot rated “passenger” with 115 hours total flight time. They’re operating 100 feet above the waves on an aerial photo mission, photographing boats. The wind in Miami, 13 miles away, is from 120 at 13 knots and it’s 26°C with a dew point of 21°C, resulting in a balmy 74% humidity.
The pilot had just completed a 180° turn to the south when the low rotor RPM horn sounds.
The pilot adjusts the throttle to compensate — in other words, we should assume that he adds throttle. The horn stops blaring, but 3 seconds later, it does it again.
So what does the pilot do? Despite the fact that the helicopter does not have floats, he enters an autorotation. The helicopter crash-lands in the ocean, the occupants escape, and the helicopter sinks. The pilots are rescued 10 minutes later by a privately owned boat. The helicopter is left unrecovered (so far) in 150-250 feet of seawater.
What We Don’t Know
There are a few things we don’t know that could explain the reason for the low rotor RPM horn:
- How much did the pilots and their equipment weight? An R22 Beta (not Beta II) is a very small helicopter. Although they had burned off 45 minutes of fuel, there is a possibility that they were still heavy for the flight conditions.
- Which direction did they turn? A turn that would have put them into a tailwind situation — especially at low speed — could rob them of airspeed. If airspeed dropped below ETL, the helicopter would have to work harder to stay in the air.
- What speed were they operating at? Without the benefit of forward airspeed and effective translational lift, the helicopter would have to work harder to stay in the air. If the speed was close to zero, the aircraft might have gotten into a settling with power situation. The natural (but incorrect) reaction of increasing the collective to arrest the rate of descent could have triggered a low rotor RPM warning if available power was exceeded.
- Were the engine and its components functioning properly? If the engine or magnetos were not performing to specifications, the resulting reduction of engine power could cause a low rotor RPM horn. We have to assume the engine was still running because the NTSB report didn’t mention an engine failure.
But regardless of the reason for the low rotor RPM horn, it’s the pilot’s decision to perform an autorotation to into the ocean that needs to be questioned.
The Robinson Low Rotor Horn
In a Robinson helicopter, the rotor RPM green arc is 101% to 104%. (Please don’t ask why; I don’t know. Yes, it is weird.) The low rotor RPM warning system is designed to alert the pilot at 97% RPM. (See it in action for yourself here.) This is a very early warning. The idea is that if rotor RPM is deteriorating, once it gets past a certain point, it could could become unrecoverable very quickly. The earlier the pilot is warned, the better off he is.
At the Robinson factory safety course — and, one might assume, at many flight schools that train in Robinsons — pilots are taught that a Robinson can generally fly at an RPM of 80% plus 1% per 1000 feet of density altitude. Given the temperature, dew point, altitude, and altimeter setting (30.01), the density altitude was 1,612 feet. That means that the helicopter should have been capable of flight when operating at only 82% RPM.
I need to stress here that this is a general rule of thumb. Do not attempt to fly around at low rotor RPM to test this. While it’s true that my flight instructor at the Robinson safety course had me fly for a few minutes in the Long Beach, CA area at 90% RPM with the horn blaring just to prove that flight was possible, RPM is not something we play with in non-training situations. The formula is simple: RPM = life.
Low Rotor RPM Emergency Procedures
The Robinson R22 Pilot’s Operating Handbook is quite specific on what to do in the event of a low rotor RPM warning. On page 3-10, in the red-tabbed “Emergency Procedures” section, it states:
A horn and an illuminated caution light indicates that rotor RPM may be below safe limits. To restore RPM, immediately roll throttle on, lower collective and, in forward flight, apply aft cyclic.
The NTSB report indicates that the pilot initially “adjusted the throttle to compensate for the [low rotor RPM warning] condition” and was immediately rewarded with recovery. But that was followed by the horn sounding again only 3 seconds later.
It had to be scary for the pilot. After all, he’s only 100 feet above the water and he’s supposed to react by lowering the collective. But the emergency procedure and repetitive training doesn’t tell us to enter an autorotation, which would be a full-down reduction of the collective. The reduction of the collective, coordinated with the rolling on of the throttle, should be slight — perhaps an inch or so. This reduces drag on the blades while the increased throttle provides power to increase their RPM.
What Was the RPM?
One of the things we don’t know is what the RPM was when the pilot decided to enter autorotation. If it had deteriorated to the point where autorotation and cyclic flare were the only tools to recover RPM, his decision was probably a good one. Better to hit the water relatively softly than from 100 feet up, falling like a brick.
If RPM had deteriorated to that point that quickly, however, it’s important to recover the aircraft to learn why. Other than a complete engine failure — which was not mentioned in the report — it’s hard to imagine what would cause RPM to drop enough to warrant such a drastic recovery action.
Who Was Flying?
There may be more to this than what meets the eye.
The helicopter was operated by Helicopter Academy, a flight school with locations across the U.S. The school’s Web site clearly advertises it as a low-cost training company:
$250 PER HOUR R22 HELICOPTER TRAINING TIME BARGAIN and we are the ONLY company in the world that can guarantee you a job. We operate a fleet of helicopters and like other schools our insurance requires 300 hours helicopter time and an instructor’s rating to fly for us. We train you to work for us and offer a job to all graduates, including transfer student and instructors who can’t get jobs elsewhere.
Helicopter Academy’s other business is BoatPix, which uses helicopters to photograph boats and then sells the photos to the boat owners and others. It’s widely known that BoatPix pilots pay BoatPix (or Helicopter Academy) for the time they fly aerial photo missions. The company’s Web site alludes to this:
…you pay for the first 100 hours at $250/hr, the second 100 hours at $200/hr and the third 100 hours at $150/hr….It’s $25,000 for the first 100 hours where you’ll do mostly training, $20,000 for hours 100 through 200 where we’ll introduce you to our photo contract which will subsidize your flying and $15,000 for hours 200 through 300 where you’ll do almost exclusively photo and will learn this skill that is valuable to our photo contract and making you a valuable pilot to us.
I added the emphasis in the above quote. It begs the question: who was actually flying this aircraft? The NTSB report suggests that it was the
600-hour CFI. But was that really the case? Was the 115-hour private pilot paying $200/hour to be “introduced” to the photo contract — as a pilot — while the 600-hour CFI took the photos?
High Risk Operations
In March 1999, Robinson Helicopter issued Safety Notice SN-34. The latest version of this Safety Notice is dated April 2009. Titled “Aerial Survey and Photo Flights – Very High Risk,” it starts out saying:
There is a misconception that aerial survey and photo flights can be flown safely by low time pilots. Not true. There have been numerous fatal accidents during aerial survey and photo flights, including several involving Robinson helicopters.
It goes on to list some of the possible dangers of low time pilots conducting aerial photo flights. It also makes some recommendations for minimum requirements for aerial photo/survey pilots, including a minimum of 500 hours pilot-in-command. BoatPix is one of the operations that has chosen to ignore this recommendation.
My question to helicopter pilot wannabes out there: Are you that desperate to become a pilot that you’re willing to trade your safety for flight time?
Pilot Experience and Decision-Making
What it all comes down to is whether the pilot made the correct decision for the situation he found himself in. I’m not convinced that entering autorotation over the ocean on hearing a low rotor RPM warning horn is the correct decision.
True, both pilots walked (or perhaps I should say, swam) away. But if the rotor RPM could have been brought back into the green while in flight — something a well-trained or experienced pilot could have accomplished if there wasn’t a mechanical problem — the watery autorotation and the resulting loss of the aircraft could have been avoided.
Hopefully, the Probable Cause report for this accident will shed some light on what really happened. Until then, it certainly gives pilots some food for thought.
November 1, 2011 Update: The Probable Cause report doesn’t add much to what’s reported here other than to clarify airspeed and PIC experience. The official Probable Cause is “A loss of main rotor rpm for undetermined reasons.”
Update, March 17, 2012: Just found another accident report with someone else using autorotation as a cure for low rotor RPM. He crashed, too.