3 - CAT-A procedures

[Nils]

Purpose
The purpose of category A procedures is to operate the helicopter in such a manner that, if one engine
fails at any time after takeoff or during landing, the helicopter can:
- Land safely and stop in the takeoff area, or
- climb out from the point of failure and attain stabilized single engine forward flight.

Takeoff



The Takeoff Decision Point (TDP) is determined by the height over the ground or the obstacles
surrounding the takeoff area. If you have a 60 ft building in your departure path, you are going to need to add 60ft to your TDP to be sure to make it in case of an engine failure. The nominal TDP height varies with different helicopters. For the BK-117 it's at about 140 ft.

If a one engine inoperative (OEI) condition occurs, i.e. if an engine fails, before the TDP, the emergency procedure is to set power to the One Engine Inoperative-limit, lower the nose to attain forward speed before flaring and settling down on the takeoff area. To make sure this maneuver is possible, CAT-A takeoffs are flown by taking off, reversing slightly so that the takeoff zone is visible through the helicopter chin windows and then climbing out backwards while keeping the takeoff zone in sight until the TDP is reached. During the flare and cushioning of the landing, most engine and transmission designs will allow a transient (<10-15 seconds) torque well above the OEI limit (140% TQ in the BK-117).

If an engine failure occurs after the TDP, the emergency procedure is to lower the nose to 20-25
degrees nose down, accelerate to VTOSS (Takeoff Safety Speed, about 50 KIAS in the BK-117). When reaching VY (in the BK-117, 65 KIAS), set power to OEI limits and initiate a climb.

Landing



The Landing Decision Point (LDP) is a point along the approach path where height over ground or
obstacles is about 100 ft and the airspeed around 20 KIAS.

If a single engine failure occurs before the LDP, the emergency procedure is to set power to the One
Engine Inoperative-limit, lower the nose to increase forward speed to VTOSS (Takeoff Safety). When reaching VY (best rate of climb speed), set power to OEI limits and initiate a climb.

If an engine failure occurs after the LDP, the emergency procedure is to set power to the One Engine
Inoperative-limit, lower the nose to attain forward speed before flaring and settling down on the takeoff
area.

To allow the above maneuvers, the approach must be flown with a reasonably steep vertical path and the pilot should continuously verify that speed and height over ground matches the appropriate profile.

[media]http://www.youtube.com/watch?v=pN0-fbieclc[/media]