Height-Velocity diagram for Bell 206

Throughout the country, there are many commercial helicopter operators who contract out their services, then employ pilots who are eager to build hours flying the contracted missions. But, these pilots are so eager that they tend not to challenge their boss when they are asked to fly what are clearly unsafe missions. A pair of common examples will follow, but first look at this diagram.

In this graphic example, Bell has published operating parameters for their model Bell 206, a very common helicopter. This ‘Height-Velocity Diagram’ shows which combinations of speed and altitude are considered safe, and which are considered dangerous. Essentially, the hatch-marked portions show that the helicopter needs to be operated low, over ‘smooth, level, firm’ ground, or it can be operated higher with added speed. In general, operating a helicopter at speeds under 40 mph and over 20 feet above the ground is deemed hazardous. Hover operations (with little or no airspeed), even as high as 400+ feet, are to be avoided.

Here in my corner of the country, in the Pacific Northwest, people have died flying small helicopters doing low-altitude contract flying. One typical operation is the slinging of bundles of Christmas trees from the field to staging areas, in the late Fall. The helicopters zip back and forth, rarely going higher than 100-feet altitude. Another typical operation is to ‘air-dry’ cherry trees in early Summer, flying low to blow off the morning dew, so the hand-picking crews can get to work.

As the diagram shows (and this is a typical helicopter diagram), the manufacturers clearly declare that it is unsafe to use their helicopters at altitude/speed combinations as are needed for these two common commercially contracted operations. To emphasize this point, I have added some colored marks:

  • The green dots illustrate operations considered safe: hovering at ten feet or less, and slightly higher only if some speed is added.
  • The blue rectangles illustrate safe operations at 10mph speeds at and below 10 feet AGL. These also illustrate safe operations at a 50mph speed, but only in the altitude range of 10-feet to 43-feet above the flat, firm unobstructed surface.
  • The red squares illustrate the unsafe flight conditions when slinging bundles of Christmas Trees. One square shows a combination of 10mph & 110-feet altitude; the other square shows a combination of 20mph and 65-feet altitude.
  • The orange squares illustrate the unsafe flight conditions when drying cherries with a helicopter. The left square depicts a 10mph & 15-feet altitude combination; the right square depicts a 30mph & 20-feet altitude combination.

Not depicted are the hundreds of sustained hover operations related to powerline construction and maintenance. Helicopters are hired to hover for long periods of time, positioning materials, equipment and personnel, typically at altitudes from just above the powerline to a few hundred feet total elevation. The vast majority of reported (and NTSB-investigated) contract helicopter accidents are for exactly this unsafe scenario.

There have been many fatal accidents investigated by NTSB. Despite this long history, it appears that FAA has done nothing to clamp down on these unsafe commercial helicopter operations. In the meantime, FAA continues to propose fines against airlines (few of which are ever collected), delay the safe development of drone systems, and obstruct the rights of impacted airport neighbors and truth-speaking Whistleblower employees … all while the helicopter death toll goes on.