Instrument Departures

Clearing terrain after departure

Whether I am doing an FAA Instrument Checkride, CFI-Instrument Airplane, 61.58, 135.293, 135.297, or a 121.141 proficiency check, I see pilots struggle with Standard Instrument Departures (SIDs) and Obstacle Departure Procedures (ODPs). The standard instrument departure is based on a minimum climb gradient of 200 feet per nautical mile (NM). However, when a SID or an ODP shows a minimum climb gradient of, say, 310 feet per NM, I ask the student if that is higher or lower than the standard climb gradient. I have been dismayed that nearly half of the responses are wrong. So, I thought we should take a closer look at this topic. This subject gets even more confusing when we discuss One Engine Inoperative (OEI) or engine out procedures.

Standard Instrument Procedures
Standard Terminal Instrument Procedures (TERPS) typically assume a climb gradient of 200 feet per nautical mile (unless a greater climb gradient is specified). This means that for every one NM (6076 feet) the airplane moves forward horizontally, it needs to climb 200 feet vertically. During development, departure procedures first look for an obstacle clearance based on a 40:1 ratio. This is about one foot of obstacle rise for every forty feet of horizontal distance or the length of a school bus. At mile one, the highest obstacle can be 152 feet. Then, the FAA TERPS adds 48 ft/NM to come up with the standard climb gradient of 200 ft/NM. At two nautical miles horizontal distance, the highest obstacle may be 304 feet (adding another 152 feet to the obstacle height for each NM of horizontal distance) and another 48 feet for obstacle clearance. Straight-out obstacle 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 departure 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.

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.

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 enroute 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 instrument 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 indicates 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 gradient 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). The FAA “low, close-in obstacles” are referenced with the ODPs in the “TAKEOFF MINIMUMS, (OBSTACLE) DEPARTURE PROCEDURES, AND DIVERSE VECTOR AREA (RADAR VECTORS)” indicated with a non-standard takeoff negative “T”.
3. Weather minimums can be increased to see and avoid obstacles while climbing in visual conditions. This can be seen on the Jeppesen Chart No. 10-9A (KPSP). The Take-Off & Obstacle Departure Procedure for Runway 13R at KPSP indicates that you may “Climb in Visual Conditions” using standard climb gradients if the Ceiling is 5900 feet and the visibility is 3 SM (5900-3). The FAA chart indicates the same 5900-3 in the “Takeoff Minimums, (Obstacle) Departure Procedures, and Diverse Vector Area (Radar Vectors) on page L20. This section is also highlighted by the negative “T.” By the way, Diverse Vector Area means random vector or in any direction. (A Diverse Vector Area (DVA) has been surveyed by the FAA and meets all ODP criteria for departures, obstacles and terrain sufficient to allow the controller to issue radar vectors within the coverage of the DVA. They also allow for radar vectors below the controller’s normal Minimum Vectoring Altitude (MVA)).
4. RTRL-Reduced Takeoff Runway Length. In our example at Arkadelphia, Arkansas (KADF), takeoff notes for Runway 4 state: “Alternatively, with standard take-off minimums and a normal 200 feet/NM climb gradient, take-off must occur no later than 1900 feet. prior to the departure end of the runway.” In this example, if we start our climb early and are well above the normal minimum of 35 feet above the departure end of the runway, the runway provides additional obstacle clearance. We do not need to comply with the increased climb gradient of 237 feet/NM to 400 feet.
5. VCOA-Visual Climb Over Airport to the enroute structure. You must obtain ATC approval or advise ATC at non-towered fields. Circle over the airport and avoid the obstacles visually until you get to the enroute segment. At Reno Tahoe International (KRNO), the SPARKS 1 OBSTACLE DEPARTURE for all North and South runways requires a 3200-foot ceiling and 3-mile visibility for a Visual Climb Over Airport. Be advised that the 3200 feet is AGL (not MSL), or the ceiling would be below the airport elevation of 4415 feet.
6. Procedure/Route. A route or heading to avoid the obstacles is a common course of action to comply with a SID or ODP. Boyne Falls, MI/Boyne Mountain Airport (KBFA) states that for runway 17, you need to climb, heading 175 degrees to 1400 feet, before proceeding on course. This is, of course, so you do not fly into the mountain. The procedure may be a simple heading like at Boyne Falls or much more detailed such as at Aspen, Colorado (KASE) runway 35, LINDZ 9 Departure that has a much more detailed route, altitude restrictions, and a 465 feet/NM climb gradient to 10,000 feet.

The word “Standard” or “STD” by itself is usually a reference to the standard takeoff minimums requirements. They are referencing the required visibility only. These are applicable to Part 121 and 135 operations but do not apply to Part 91 operations. The standard requirement for airplanes with two engines or less is 1 SM. The standard requirement for operations with three engines or more is ½ SM. Part 91 pilots are allowed to assume more risk, so the requirements do not apply to them. Now, we have all seen airliners take off with much less visibility than these. Operation Specifications allow Part 121 and 135 operators to have lowered minimums if trained and approved by the FAA. Most operators train to 500 RVR, but only on long runways with full lighting systems, including centerline lights. If a visibility limitation is listed in other areas, such as 3 SM for a VCOA, it becomes a limitation to Part 91 operators as well as commercial operators (parts 121 and 135).

SIDs need to be issued by ATC to fly them. You may not fly a SID without a clearance. ODPs are not issued by ATC except in some cases for traffic separation. It is helpful to ATC if you advise them that you will be flying an ODP. It will also be very helpful to you by guaranteeing you terrain and obstacle avoidance, something most pilots are highly fond of.

Some Gotchas

The RUUDY SIX RNAV Departure at Teterboro, NJ (KTEB) for Runway 24 indicates a top altitude of 2000 feet. However, the plan view and the notes both indicate a mandatory altitude of 1500 feet to cross WENTZ Intersection and then resume the climb to 2000 feet after passing WENTZ Intersection. Many pilots have busted this altitude by setting 2000 feet, hand flying, or just not paying detailed attention to the quick level-off required for this departure.

The SQUAT FIVE RNAV Departure at Rifle Garfield Airport in Rifle, CO (KRIL) for Runway 26 directs you to fly 26 NM down the valley toward the Southwest to SQUAT Intersection. This SID is also listed as an ODP. The ODP for Runway 26 states to “use SQUAT DEPARTURE.” I had two clients/jet student pilots who received an FAA violation for departing from their planned flight. There is not a control tower at KRIL, so the pilots took off with a clearance void time. They advised Denver Center that they were flying the SQUAT FIVE Departure. ATC said “OK”, so this departure procedure became part of the crew’s most recent clearance. (There were likely more words, but I do not have the tapes). When the crew was at a safe altitude, but not to SQUAT Intersection, they made a turn to the East (Red Table/DBL VOR) as that was the direction of their destination. Remember to let ATC know before deviating from a flight plan, even if it was not your originally filed flight plan.

In our third example, a crew was flying out of Denver, CO (KDEN) and cleared from Runway 16R with a “Climb Via” the EEONS EIGHT RNAV Departure. The top altitude is listed as FL230, so the pilots set this number into the airplane’s altitude selector for the autopilot. The departure has you cross GISTT Intersection at or above 7000 feet, but it next states to cross KIDNG Intersection at or below 10000 feet. My clients were new to the jet and not comfortable with the use of the “new to them” VNAV button on the autopilot’s flight control panel. So, they used the Vertical Speed (VS) button to climb and busted the altitude restriction of 10000 feet at KIDNG Intersection by several thousand feet. They could have set 10000 feet in the altitude selector until passing KIDNG Intersection.

I will end this article by quoting a paragraph from the FAA’s Instrument Procedures Handbook pg. 1-43 that ends with a strong statement:

When planning for a departure, pilots should:

• Consider the types of terrain and other obstructions in the vicinity of the airport.
• Determine if obstacle clearance can be maintained visually or if you need to make use of a DP.
• Determine if an ODP or SID is available for the departure airport.
• Determine what actions allow for a safe departure out of an airport that does not have any type of DPs.
• By simply complying with DPs in their entirety as published, obstacle clearance is guaranteed!