AW139 Approaches With MAP Offset From Runway
For AW139 operators, Service Information Letter (SIL) D201704000013 describes the following condition pilots should be aware of: Approaches that have the Missed Approach Point (MAP) located at a position other than the runway or where the MAP is not the last waypoint of the approach will use the last waypoint (the runway – or helipad for helicopter approaches) as the MAP. As a result, the rest of the missed approach will sequence differently than the published missed approach course and will not guarantee obstacle clearance. Figure 1 shows an example helicopter approach where the MAP and the first missed approach waypoint are not aligned.
|Figure 1. MAP and First Missed Approach Waypoint Not Aligned|
This condition occurs due to an interpretation by the software logic that inserts a runway (or helipad) into the flight plan as the last lateral waypoint. Because most approach MAPs are located either at the runway or as the last waypoint of the approach, this type of approach is not commonly seen by pilots. For these approaches, the FMS uses the last lateral waypoint – which is not the MAP – as the beginning of the missed approach flight plan computation. Doing so results in a course and distance of the first leg of the missed approach, as well as subsequent altitude legs, that deviate from the published missed approach and should therefore not be flown.
When the MAP, the last waypoint of the approach, and the first missed approach waypoint line up, the issue may not be noticeable. However, when the course from the MAP to the first missed approach waypoint differs significantly from the course from the last waypoint to the first missed approach waypoint, the issue is more pronounced. The YXMO R194 Copter approach shown previously in Figure 1 illustrates such a case.
This condition described in the SIL affects all AW139 Epic phases, including phase 7. Figure 2 shows Phase 7 MCDU flight plans before and after executing the missed approach.
|Figure 2. MCDU Phase 7 Missed Approach Flight Plans Before and After Activation|
On the left (prior to the MAP) the FMS is predicting a 042 course to XMONH, the first missed approach waypoint. This is due to FMS logic assuming the aircraft is traveling at 250 knots. At that speed, the aircraft will have overflown the MAP and would have to make a much more pronounced turn to the left (northeast) in order to reacquire the published course of 114 degrees. The rest of the flight plan on the left is compliant with the missed approach instructions. The MCDU depiction on the right illustrates the missed approach flight plan after it has been activated. Using the current aircraft speed, the 250-knot assumption is now replaced with a truer depiction of the published missed approach. Passing the Final Approach Fix (FAF), the aircraft will turn to a 122-degree course after crossing the MAP, but (as the reader can observe) an incorrect course is inserted between the XMONH first missed approach waypoint and the altitude constraint.
It is important for pilots to always review the flight plan on the MCDU against the charted procedure. For the AW139, missed approaches with the described profile should be reviewed in advance and pilots should expect to manually fly any segment that doesn’t appear to comply with the charted and published procedure.
Please contact Honeywell Flight Technical Services with any questions or operational issues.
Rob Erlick is a Program Pilot with Honeywell Flight Technical Services. He can be reached via email at Robert.Erlick@Honeywell.com.