SEARCH What's New

Spiral dive sometimes called death spiral

 

As with stalls and spins, we should be teaching students how to identify the situations where spiral dives may occur. Spiral dives are most often not identified until it is too late for recovery.

One of the two most common spiral dive situations occurs shortly after inadvertent cloud entry. The aircraft pitch attitude may be level when the aircraft very gently starts to roll into a turn. A turn of three degrees per second or less may not be noted by the inner ear. If this turn is left unchecked, the aircraft nose will fall over into a descent, airspeed increases and a spiral dive will begin.

The aircraft pitch attitude may be slightly high at cloud entry and if it is allowed to pitch up even slightly more, the airspeed will begin to decrease. The high pitch attitude of the aircraft and the decreasing airspeed will cause the aircraft to yaw to the left and if this is not recognized, the yaw will cause the aircraft to gradually roll to the left. The aircraft nose will fall into a descending turn and the spiral dive cycle begins.

Both of these situations are insidious as nothing is felt by the pilot until the spiral dive is well underway and the acceleration into the turn causes the “G” forces to increase. We may not notice we are out of control until we exit cloud, which may be too late.

In cloud, we may mistake the information given by the instruments as a spin. The key difference is the airspeed. The airspeed will be near the aircraft stall speed and stable in a spin, and increasing in a spiral dive.

A pilot of a C-182 inadvertently flew into cloud during a flight from Castlegar, B.C. to Vernon, B.C. He contacted Vancouver centre and tried to turn around. The centre controller shortly thereafter watched on radar as the aircraft descended into the terrain. The finding of the TSB was that the pilot lost control of the aircraft and entered a spiral dive and crashed into the top of a mountain.

The pilot of a C-172 was flying along the Coquahala Highway in B.C. in deteriorating weather when the pilot inadvertently flew into cloud. The pilot immediately started a 180 degree turn to return to VFR conditions. When he regained sight of the ground, he was in a spiral dive. He was able to recover in time, just.

The other spiral dive situation occurs during low level sightseeing. We may steepen a turn to look at something interesting and the aircraft pitch attitude drops, the airspeed increases and a spiral dive begins. This type of situation is seldom recoverable. A father and son were sightseeing over a new housing development in a Cessna C-152. Observers saw the aircraft in a sustained turn and then the aircraft started to descend gradually at first and more steeply. The aircraft struck the ground in a steep descent under full power.

Inadvertent loss of horizon situations such as the one encountered by John Kennedy Jr. are the reason why five hours of instrument training is required for the private pilot licence.

The instant a loss of horizon condition exists or inadvertent cloud entry occurs, it is imperative to transition to the instruments. A level turn should be carefully initiated through 180 degrees to exit the loss of horizon or IFR condition as soon as possible.

In some cases, it may be logical, depending on terrain, to commence a wings level descent out of cloud. This is no time to get fancy. Unless we are proficient instrument rated pilots, we should do just one thing at a time, turn or descend. More may be beyond our capabilities in a high stress situation.

We must also remember that the loss of horizon or inadvertent cloud entry may result in disorientation and make the transition to instrument flight very difficult. The concentration to fly on the instruments will be very difficult to achieve.

If disorientation does occur, we must force concentration and believe the instruments no matter what sensations we feel physically. If we try to fly by the seat of our pants, a spiral dive will almost certainly occur.

The recovery for a spiral dive is:
Power to idle,
Roll the wings level,
and
Pull out of the dive.

The power must be moved to idle quickly to reduce the accelerating forces downwards and into the turn. The wings must be rolled to level as quickly as possible to get the lift vector up for an efficient pull up and to eliminate the horizontal component of lift pulling us into the spiral dive.

The fastest way to roll out of the turn is with coordinated aileron and rudder. The pull out of the dive will be as hard as necessary to avoid the ground.

While practicing this manoeuvre, we must try to avoid pulling up while we are still rolling the wings level. The combination of roll and pull up results in rolling “G” or torsional stress, which non-aerobatic aircraft are not well equipped to handle.

We have a tendency once we get our licences to go out and play, and to forget to occasionally practice our basic instrument skills. When needed, these skills may no longer be there.

The moral of this story however, is to avoid getting ourselves into situations where we may lose the horizon and possibly our situational awareness, and to avoid low level sightseeing or showing off.

We are too often too aggressive in our desire to get where we want to go, or we are overconfident in our ability to fly in marginal conditions.

There is a reason a spiral dive is sometimes called a death spiral.

Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently manages a small airline and teaches part-time for a local aviation/university program. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.