Winter Flying: "Weatherproofing" Against Inadvertent IMC

By Terry Terrell, Atlanta | February 1, 2008
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A handful of techniques can help protect VFR operations from the hazards that arise from winter conditions.

As an operator and participant, I have led emergency medical service (EMS) helicopter activities here in Atlanta since 1986, through several organizational incarnations. Most recently, our privately owned Georgia Baptist LifeFlight/Rescue Air 1 programs were flattered with having been acquired by Omniflight, Inc.

Within the context of this background, I found myself reading EMS pilot Brian Swinney’s comments on his accident, and the lessons he drew from it about the importance of instrument flight rules (IFR) training and proficiency, with great interest ("A Personal Encounter With IMC," October 2007, page 48).


For much of my military career, I enjoyed the privilege of flying the remarkably versatile U.S. Coast Guard Sikorsky HH-3F (S-61). Our training in that very sophisticated helicopter focused heavily on comprehensive IFR operations. During the 1970s, in fact, we were beneficiaries of what was reputed to be the most advanced helicopter instrument simulator in the world at the time, at CGAS Mobile, Ala. I remember transitioning to the H-3 there and not seeing an actual airframe until my third week of training. We walked out on the ramp and did our first preflight inspections. Then I flew an entire mission, never having touched an actual H-3 before, but having spent two weeks in an astonishingly realistic full-motion instrument simulator, with no visual system whatsoever.

So I admit to an advantaged background in helicopter instrument operations. Yet even with this level of seemingly optimum exposure, I have occasionally been challenged by the risk of inadvertent instrument meteorological condition (IMC) encounters in civilian EMS settings. As check airman over most of LifeFlight/Rescue Air 1’s operational years, I always tried to place special emphasis on response to unexpected IMC encounters, attempting to keep everyone in our programs as prepared as possible for dealing with such a serious threat.

Unfortunately, helicopter pilots and their crews and passengers seem destined to indefinitely pay the price for inadequate preparation against the inadvertent IFR threat. One recent case may be the Dec. 3, 2007 crash of a Eurocopter BK117C1 in Alaska. The U.S. National Transportation Safety Board is still investigating that accident, so it is too early to draw definitive conclusions about its causes, but preliminary NTSB information reveals that IMC prevailed in the accident area when the LifeGuard Alaska flight from Cordova to Providence Hospital in Anchorage impacted the ocean about 3 mi east of Whittier. The pilot, paramedic, and patient on board the visual flight rules (VFR) flight were lost at sea. The flight nurse suffered fatal injuries.

Rescue Air 1 is an emergency medical helicopter activity carefully optimized for our region of the Southeast United States and our particular mix of documented mission assignments. We cannot, in the normal course of our work, routinely file and fly instrument flight plans, nor do we need to maintain program certification to do so. With few instrument approaches to hospitals, and certainly none to emergency landing zones at accident sites and residential settings, regular use of the conventional instrument environment is of little practical use for our purposes.

All of our pilots, however, are instrument-rated and experienced, most very extensively so. They also are trained to fly our aircraft to safe VFR recoveries in the event that IMC conditions are encountered unexpectedly. That is a distinct possibility throughout Georgia’s cooler months, especially in the mountains at night, where the "black hole" triangle formed by lines drawn between Atlanta, Chattanooga, Tenn., and Asheville, N.C., is often presented to us as a weather mystery.

What I submit here is a presentation of our specific strategy for recovering to a continuation of safe flight operations in the event that a flight suddenly encounters a dangerous loss of external visual flight reference.

Our "weatherproofing" approach to defense against inadvertent IMC encounters can be thought of as working in much the same way as "drown-proofing" works with regard to swimming survival. "Drown-proofing" bypasses refined swimming techniques as a training objective in favor of developing simplified but reliable, high-endurance survivability on the part of the involuntary swimmer.

With FAA support of our "weatherproofing" training program, LifeFlight/Rescue Air 1 captains traditionally have maintained what is regarded as solid IFR proficiency. This proficiency is not in fully utilizing the entire IFR system to accomplish routine navigation to regular destinations. Rather, it is aimed at reliably confirming that fundamental IFR skills exist as a standby safety option that is always instantly available in case of emergency.

As a prelude to accomplishing inadvertent IMC "weatherproofing," it must be understood and appreciated that modern concepts of instrument flight exist today as a completely refined and proven set of operational methods within all of aviation, including rapidly developing rotary-wing participation. To provide for safe and efficient emergency medical flight operations in diminished meteorological conditions, domestic helicopter instrument procedures are being standardized at a rate previously unknown outside the military.

As outlined in FAA advisory circulars, helicopter flight "when weather conditions make ground visual contact difficult or impossible, can only be conducted safely... by operation solely with reference to flight instruments." That is true whether that IMC encounter is "deliberately undertaken or inadvertently encountered."

When IMC is encountered inadvertently, and comfortable visual ground cues are lost, a pilot "should never include his trying to improvise reestablishing those visual flight environment cues," the FAA says. The pilot’s "first concern must be focused on establishing control of the aircraft by reference to the instruments, and not on attempting to regain visual contact with surface features."

Such inadvertent conditions represent "an overpowering primary hazard factor," the agency says. That, unfortunately, continues to be demonstrated again and again in what are often high-profile accidents.

Pilots must always remember that "a blind descent in instrument conditions, hoping to see the ground before impact, is aviation negligence at its very worst," the FAA notes.

Described most simply, instrument flight involves the normal conduct of flight operations by reference to instruments only, without benefit of the pilot’s reference to outside visual cues. It provides for safe, efficient navigation without threat of colliding with terrain or other aircraft.

Basic flight instruments (including attitude and heading gyros, barometric and radar altimeters, and rate-of-climb/descent, airspeed, and rate-of-turn indicators) provide for the normal physical control without visual reference outside of the cockpit. Avionics instruments, such as LORAN, GPS, and VOR and ADF radios, similarly allow for reliable and flexibly efficient, self-contained navigation capability in zero visibility. Communication radios, along with radar transponder equipment, allow instrument operations to be conducted under the supervision of air traffic control authorities, and ensure that the hazard of possible midair collision with other aircraft is minimized, though this category of risk is — with correct priority — the last to be accommodated by proper procedure for aircraft operating at typical en route helicopter altitudes.

"A blind descent in IMC, hoping to see the ground before impact, is aviation negligence at its very worst."

We can legitimately but unexpectedly encounter unplanned or inadvertent instrument flight in perfectly safe and legal VFR conditions. In our region, for instance, that’s especially true during the fall and winter months, and most especially at night along or near frontal boundaries, icing conditions notwithstanding. Weather-reporting facilities in the north Georgia mountains are limited, and terrain effects on frontal weather systems can complicate aviation weather forecasting challenges beyond conventional levels of comfort and reliability in any case.

Since Rescue Air 1 pilots are routinely tasked with negotiating winter night flying in the north Georgia mountains, proven inadvertent IMC procedures are critical to our safety. These procedures can be fundamentally expressed as "The Four Cs" — a concept previously outlined by Joel Harris in The Journal of Air Medical Transport.

The first C stands for CONTROL. This indicates that the first thing a pilot must do after losing visual reference with the ground is to establish positive control of the aircraft by reference to basic flight instruments — and solely by reference to those flight instruments.

The second C stands for CLIMB. This reminds us that the pilot must immediately initiate a climb away from terrain and obstacles, which represent by far the greatest primary threats to safety in inadvertent IMC flying at lower altitudes. Once committed to the IFR environment, the pilot must resist the temptation to consider trying to regain outside visual cues, no matter how uncomfortable the shift to instrument reference may feel. This is especially true during the initial moments of the climb.

Guessing with regard to where the terrain and obstacles might be, and hoping to avoid them or to reestablish visual contact with them, is a totally unacceptable plan for avoiding disaster. The climb should be made to an altitude that will positively ensure that all terrain features and obstacles are safely avoided. The climb also must be executed at a rate (or angle) that will eliminate all possible terrain-collision hazards until the target altitude is reached.

The third C stands for COURSE. This provides a checklist item reminding the pilot that changing the flight track over the ground, usually to the reciprocal of the original heading, will take the aircraft back to the known, acceptable weather conditions that prevailed before the inadvertent IMC encounter (by definition, just moments earlier). This 180-deg turn back to previously experienced, better weather must be executed only after confirming that immediate terrain clearance has been accomplished. The turn also specifically should be made in the direction that will provide the greatest separation between the aircraft and the terrain.

The fourth C stands for COMMUNICATE. This finishes the checklist with an item to be used if a return to VFR conditions is not readily accomplished after the reciprocal turn. Communication with ATC can, in some cases, allow an IFR clearance to be requested and issued, either back to VFR conditions, or, if necessary, to an instrument approach termination.

The conscientious pilot should never expect to need to take full advantage of the whole "Four Cs" scenario, terminating with a full instrument approach. That situation — of being forced to return to an airport ILS and executing an approach to minimums — would imply a problem with the pilot’s preflight weather awareness beyond excusable limits in the first place.

But if inadvertent IMC is experienced, the Four Cs must be considered key to safely negotiating such circumstances and to accomplishing good "weatherproofing" protocol and a safe recovery.

Inadvertent IMC is not something we should expect to see often, even during winter months. But conscientious pilots and operators must be prepared to deal with such encounters whenever they may occur, in a reliably disciplined and practiced manner.

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