Page 11 - Feb24T

and another 48 feet for obstacle clearance. Straight-out ob- stacle clearance is provided within 500 feet of each side of the runway centerline at the departure end of the runway (DER), then spreads out to 15 degrees. The standard depar- ture is designed to ensure required obstacle clearance to a minimum of 1000 feet in non-mountainous areas and 2000 feet in mountainous areas. The procedure is also based on the airplane crossing the departure end of the runway (DER) by at least 35 feet and climbing to 400 feet above the DER elevation before making any turns. Chapter One of the FAA Instrument Procedures Handbook is an excellent resource for studying this topic.
Pilots can avoid these obstacles by 1. increasing weather minimums to “see and avoid” and maneuver around them; 2. incorporating a greater climb gradient to cross above the obstacles; 3. following a specific departure route to avoid the obstacles.
So, what happens if an obstacle penetrates the 40:1 ratio or is higher vertically than the 152 feet allowed for each nautical mile?
Here are six methods to comply with a SID or ODP.
1. Standard Climb Gradient 200 ft/NM
2. Non-standard Climb Gradient-gradient more than 200 ft/NM
3. Non-standard weather minimums-i.e., 1200-3
4. RTRL-Reduced Takeoff Runway Length
5. VCOA-Visual Climb Over Airport to the en route structure
6. Procedure/Route
Here are some examples of how to comply.
1. Most departure procedures apply the standard climb gradient requirement of 200 feet/NM. The FAA only assesses the need for an ODP at airports with an in- strument approach procedure.
2. If an obstacle penetrates the standard climb gradient, TERPS can just require a steeper climb gradient to clear the obstacle. The THERMAL SIX DEPARTURE for Runway 13R at Palm Springs International (KPSP) requires a minimum climb gradient of 422 feet per NM to 2300 feet (MSL). This is a little more than twice the normal required climb gradient of 200 feet/NM. The difficult part is determining if your airplane can maintain that rate of climb by analyzing the AFM performance charts and converting the required climb in feet per nautical miles to feet per minute (FPM). Jeppesen makes it easy by printing a table on the chart of their departure procedures (SIDs) that show the required vertical speed based on the required climb gradient and ground speed (GS) (Table indi- cates 1055 PFM for 150 kt Ground Speed). For FAA SIDs and ODPs, you will have to look at the FAA Rate of Climb/Descent Table, which is located on the last page of the Digital Terminal Procedures Supplement (Must interpret the table indications between 1000 and 1130 FPM). Another way is to do some simple math. GS x feet per NM divided by 60 = FPM. (150 x 422 = 63,300 divided by 60 = 1,055 FPM). It becomes much more difficult with steep climb gradients to a higher altitude, such as the Truckee Tahoe Airport (KTRK) TRUCK FIVE Departure from Runway 29 that requires a climb to 11500 feet with a climb gradi- ent of 500 FT/NM. For “low, close-in obstacles” with Jeppesen, you will have to look at another page, “TAKEOFF OBSTACLE NOTES” (KPSP pg. 10-3OBA1).
Clearing terrain after departure
Low, Close-in Obstacles
Of course, there are exceptions to most rules, including standard climb gradients. TERPS does not provide the standard obstacle clearance for what they call “low, close- in obstacles.” These are obstacles within one NM of the departure end of the runway (DER) and are less than 200 feet above the DER elevation. This is to prevent publishing excessive climb gradients for these low, close-in obstacles. These obstacles are noted in the departure procedures, so the pilot may identify and avoid them. These are the multitude of entries titled “TAKEOFF OBSTACLE NOTES” that are listed in the Departure or Takeoff Minimums/ Obstacle Departure Procedures area of the charts. These “low, close-in obstacles” also have consequences to approach minimums, but we will save that for another time.
February 2024 / TWIN & TURBINE • 9