Archive for October, 2009

Bad ideas

Wednesday, October 28th, 2009

There are some things that helicopter pilots do that are just not smart.

For example the pilot of a Robinson R22 Beta landed in a field to pick up some equipment and while he was there he decided to hot refuel. The pilot’s father drove a pickup truck equipped with an auxiliary fuel tank under the rotor disk of the running helicopter to accomplish the refueling. The pilot said he stayed at the controls of the helicopter and a wind gust caused the main-rotor blades to flex down, striking the top of the truck. Although no one was injured, the helicopter rolled to the right and into the truck resulting in structural damage to the helicopter. At the time this happened winds were reported from 170 degees at 18 knots, gusting to 25.

Another bad idea is leaving the cockpit while the engine is running and the rotor system is spinning. That’s how a pilot damaged an Enstrom 280X after landing in a corn field and getting out of the helicopter. In an interview with the NTSB, the pilot stated a gust of wind appeared and the main rotor severed the tail boom.

Another pilot preparing to lift-off in an S76 noticed a “door unsecured” indication on the instrument panel for the left cabin door. He brought the engines to idle and exited the cockpit to check the door. He re-closed the door and returned to the cockpit. However, the door open annunciation came on again. He then left the cockpit two or three times to deal with the door. He did not recall retarding the engine power control levers to ground idle before leaving the cockpit the final time.

The wheel-equipped helicopter started to move as the pilot was returning to the cockpit. He told the NTSB it was moving toward the edge of the elevated helipad. He managed to climb into the cockpit, but before he could regain control, the helicopter was on its side.

I can remember several times getting ready to depart and then realizing that I needed to check or do something. It is very tempting to just friction down the flight controls and get out. However, every time I consider doing that I think of what has happened to other pilots.

Basic autopilots

Tuesday, October 20th, 2009

The majority of single-engine helicopters do not have autopilots installed. The few that do have autopilots (not counting experimental designs) use a series-parallel model. Even a simple two-axis system without a flight director can be somewhat complicated as it will have a series actuator and a parallel actuator for both pitch and roll.

In the case of the Sagem autopilot, the series actuator is known as a SEMA (Smart Electro Mechanical Actuator), the flight control tube is cut and the actuator inserted. SEMAs are fast moving with limited authority (plus or minus 3.5 mm). The parallel actuator is called a trim actuator and is normally attached to one end of the flight control tube.

 

 

 

 

 

 

 

When the pilot engages the pitch-and-roll switch, the two SEMA actuators (one for pitch, one for roll) provide a SAS (Stability Augmentation System) by making very small rapid movements that enhance stability through rate dampening. When the force trim switch is engaged, the two trim actuators will hold the cyclic control in that position. The trim actuator contains a spring-and-clutch mechanism that provides the force trim. If the pilot moves the cyclic control it will want to return to its original position.

The autopilot’s upper modes allow it to hold heading, a navigational course, altitude, and indicated airspeed. Heading and course are controlled by roll and only one of these can be active at a time. Altitude and airspeed are controlled by pitch and only one of these can be active at a time as well. In both of these modes it is normally the SEMA actuator that controls the rotor system while the trim actuator anchors the flight controls. When a SEMA is operating off its midpoint, the trim motor is activated to move the cyclic in the appropriate direction and amount to cause the SEMA to return to its center position, restoring full authority.

The autopilot computer receives data on airspeed, altitude, heading, and course and compares it to the value selected by the pilot. If there is a deviation, the autopilot computer sends the appropriate signal to the actuators which moves the rotor system in a direction to cancel the deviation. This allows the autopilot to maintain heading or course and altitude or airspeed.

This describes a very basic system. More advanced helicopter autopilots have flight directors, yaw servo actuators, and servo actuators that control the collective. There are also systems that will auto hover.


 

 

 

 

Added pressure

Tuesday, October 13th, 2009

Inadvertent IMC accidents are a problem for helicopter EMS operations. Unfortunately, when the weather is bad sometimes the pressure to accept a flight can rise. The following illustrates what I mean.

According to the NTSB, on the night of Jan. 10, 2003, an air medical helicopter was dispatched from Salt Lake City to Wendover, UT (just more than 100 miles to the west).

After departure, the pilot contacted the Salt Lake City (SLC) air traffic control tower and requested an I-80 transition low-level westbound to Wendover. The tower instructed the pilot to hold east of SLC because of landing traffic. The pilot held at 700 ft agl for about 19 minutes while monitoring the tower and the ATIS frequencies. The pilot stated the weather drastically changed from two-mile visibility to 1/16-mile in fog. Because of the deteriorating weather, the pilot elected to abort the flight and return to the hospital. Returning to the dispatch center, he heard personnel discussing that another air medical service was attempting the flight. The pilot then contacted the other pilot on the radio and reported that he just aborted the same mission because the visibility had reduced to 1/16 miles. The other pilot stated he was going to try to get over the fog.

The other pilot contacted SLC tower for a departure clearance from the hospital. He was cleared to proceed toward SLC. The pilot requested a clearance to 7,000 or 8,000 feet. He was cleared for the ascent and instructed to remain east of SLC. The pilot reported that he attempted to climb; however, he would lose VFR and requested not to do that, but to transition through the SLC airspace to see if it cleared up any better. The tower advised the pilot that the visibility was 1/16-miles and to proceed inbound and remain east of SLC. The tower then asked the pilot if he could continue westbound and the pilot responded, “I’d like to give it a try if I could.”

The tower cleared the flight westbound with instructions to maintain VFR at or below 5,000 feet. A few minutes later the pilot stated he was on the west side of the airfield, and requested to return back to the east. The controller informed the pilot that she could not let him go east until he could see other aircraft on final approach to Runway 34R or she had a break in traffic large enough to get him back to the east side.

While holding, the pilot had the following conversation with his dispatch center:

“We are on the west side of the airport,” the pilot said. “Air Med got sent out for this same damn thing and then they called us to go out. Air Med turned around for low visibility, so they go shopping for another helicopter and we’re turning around at the west side airport. You know, it what’s their determination, you know.”

“I understand,” the dispatcher said. “Unfortunately, that happens all day long. A lot of the dispatch centers do it, but, so I understand that you are turning back 20.”

“I mean, they need help,” the pilot replied.

A few minutes later, the pilot told the tower, “I’m basically inadvertent IMC at this time and declaring an emergency.” Twelve seconds later, the tower asked the pilot whether he had Runway 34L in sight.

“That’s negative and I’m currently on a heading one-five-zero,” the pilot responded.

The tower instructed the pilot to turn right to a heading of 340 degrees for a vector toward SLC. The pilot did not acknowledge the instruction, and the tower controller again attempted to contact him. No further communications were received. The Salt Lake City police department received a 911 call from a witness reporting, “Very thick fog…the helicopter barely missed their trailers…fog is very thick can only see 40 feet ahead.”

The Agusta A109K2 twin-engine helicopter was destroyed when it impacted terrain while attempting to maneuver in dense fog. The instrument rated commercial pilot and the flight paramedic were fatally injured, and the flight nurse was seriously injured.

Thoughts on IFR HEMS

Tuesday, October 6th, 2009

Most helicopter EMS programs operate under VFR only. With the high number of weather-related accidents lately, the question of mandating IFR operations is talked about a lot. I do not know of a study that compares weather-related accidents for VFR-only versus IFR helicopter EMS programs. My guess would be that IFR programs would have a lower rate of these kinds of accidents.

I have flown for two IFR programs, Mayo One (BK117 C1) and CareFlite Dallas (Augusta 109E). In both programs the pilots in general were more comfortable flying in lower weather. This is for several reasons, but mainly the extra training and the fact that they were flying a fully IFR-certified helicopter. Also, I think being IFR trained and experienced helps pilots make better go/no-go weather decisions.

Filing an IFR flight plan does take a few extra minutes. However, using the IFR system to respond to a trauma call (flight on a highway for example) is rarely done. In these cases the ground crew would have to transport the patient to the closest instrument approach (normally an airport). If we couldn’t save any time, we would advise the dispatcher that transport by ground would be faster. Time is critical and a responsible pilot must make sure not to risk delaying patient care. I seldom launched on a flight under IFR.

However, there were several times when after departing VFR and on the return flight to the hospital weather deteriorated. I would call approach and receive an IFR clearance and vectors to the hospital’s GPS approach. In general, I’d say that getting a pop up clearance was not a problem and caused minimal if any delay. Keep in mind this was Rochester, Minnesota; ATC was not as busy as some larger airports and very accommodating to Mayo One. In Dallas/Fort Worth (CareFlite) ATC was much busier but also very helpful. Here pilots are sometimes asked to turn to a different heading and may be asked to maintain VFR for a short period. Normally they will get you in the IFR system and to an instrument approach with minimal delay.

The IFR system is definitely more fixed-wing friendly. Compared to airplanes, helicopters operating under IFR is still relatively new. The development of low-level GPS routing and WAAS approaches will help change that in the future.

In general, I do not think EMS programs are able to justify the added cost of an IFR program by the increased number of flights (therefore revenue) that IFR capability brings. I think the more important point is the increased pilot proficiency it provides and the extra options it gives the pilot. In an industry that is always trying to cut costs I think highly of the programs that understand the benefits and increased safety that an IFR program brings. If I were to return to EMS flying I would definitely want to fly for an IFR program.