Secrets of Safe Departures

Even VFR pilots should know about instrument departure procedures

November 1, 2005

The pilot was in a hurry. Because he had an IFR-clearance-void time to make, he urged his wife and child along as they made the requisite preflight stops at the rest rooms and vending machines. A short time later, with a tailwind estimated to be 15 to 20 knots and a ceiling estimated to be 800 to 1,000 feet overcast, the family departed in its Cessna P210N straight out from Runway 19 at Morrisville-Stowe State Airport in Vermont.

They were headed for Harrisburg, Pennsylvania, 320 miles south-southwest, but flew only eight miles before striking trees on the crest of Mount Worcester. The airplane came to rest 200 feet below the crest on the south face of the mountain. The family of three and its dog perished in the crash.

Airplane and treetops were brought together by the pilot's failure to use what seems to be one of aviation's best-kept secrets — the published instrument departure procedure. These runway-specific procedures are created to provide an obstruction-free flight path from takeoff to the en route airway structure and often are overlooked when pilots are preparing for an IFR flight.

Departure procedures

The departure procedure at Morrisville-Stowe that the accident pilot should have flown calls for a climbing right turn direct to a nondirectional radio beacon (NDB) 2.3 miles northeast of the airport. That was opposite to his direction of flight. Upon reaching the NDB, departing aircraft enter a holding pattern while climbing to 3,500 feet before proceeding on course. Had the accident pilot complied with the departure procedure, it would have placed the aircraft above the terrain that it struck — the very purpose of an instrument departure procedure.

Two types of instrument departure procedures exist — the obstacle departure procedure (ODP) and the standard instrument departure (SID). Each type is runway specific and will assure terrain clearance if flown correctly.

The ODP is created to provide a flight path that avoids obstacles in the terminal area after takeoff. The SID is created at busier airports primarily to reduce pilot and controller workload by charting standard instrument routings out of the terminal area, but a SID also may provide a method of obstacle clearance.

The ODP is usually published in a text-only format that describes how to fly a flight path that will keep the aircraft safe from obstacles after takeoff. A few complex ODPs are published in graphical format. SIDs are always published in graphical format.

Jeppesen makes ODPs and SIDs less of a secret because it files them with all of the other instrument charts for your departure airport — all you have to do is use them. If an ODP has been created for your departure airport, Jeppesen publishes it on the 10-9A page or the 11-1 airport taxi diagram in a table titled "Take-Off & Obstacle Departure Procedure." If a SID has been produced for your airport, Jeppesen puts it on its own 10-3 page.

Pilots using NACO instrument approach books have to look in two different places for ODPs and SIDs. If your departure airport has an ODP, it will be listed at the front of the book, away from the instrument charts, in a section titled "Take-Off Minimums and (Obstacle) Departure Procedures." If a SID has been published, it will be filed with the instrument approach charts for your departure airport.

Creating departure procedures

When an instrument approach is developed for an airport, the procedure designer conducts an obstacle analysis to determine whether there are obstructions in the terminal area that are a threat to departing aircraft. According to the Aeronautical Information Manual, if an aircraft may turn in any direction from a runway and remain clear of obstacles, that runway passes what is called a "diverse departure assessment" and no departure procedure will be published.

While conducting the obstacle analysis, the procedure designer assumes that departing aircraft will cross the end of the runway at least 35 feet agl and climb to 400 feet above the airport elevation before turning. It also is assumed that the airplane will maintain a rate of climb that will produce a climb gradient of at least 200 feet per nautical mile. More about climb gradients later.

If the obstacle analysis identifies obstructions that pose a hazard, the procedure designer has the following four options to choose from to create a safe flight path:

  • Establish a climb gradient steeper than 200 feet per nautical mile;
  • Establish a steeper-than-normal climb gradient with increased takeoff minimums that allow the pilot to visually remain clear of the obstacle;
  • Design a specific departure route; or
  • A combination or all of the above.

In some cases, an IFR departure from a runway is not authorized because terrain or obstacles cannot be safely avoided without visual reference.

Making the gradient

When the FAA defines aircraft climb requirements, whether for aircraft certification or instrument procedures, most times it states those requirements as a minimum climb gradient expressed in feet per nautical mile instead of a minimum rate of climb expressed in feet per minute. That's because the FAA knows that to clear obstructions, altitude must be gained over horizontal distance.

Many ODPs and SIDs specify a minimum climb gradient that must be met to safely clear obstacles. Because aircraft-climb instrumentation is calibrated in feet per minute, preflight planning should include converting the required climb gradient into a required rate of climb. The key variable in this calculation is the aircraft groundspeed during climb.

Again, Jeppesen makes the conversion process simple. Anytime a SID or ODP includes a minimum climb gradient, published nearby will be a table that shows the required rate of climb when the minimum climb gradient and groundspeed are cross-referenced.

NACO also publishes a rate-of-climb table, but there is only one in each volume of approach charts. Pilots must flip over to that table and consult it for the required rate of climb when a departure procedure includes a minimum climb gradient. The NACO table does provide a more detailed range of groundspeeds than Jeppesen.

Tables aren't the only way to convert climb gradient to rate of climb. An E6B flight computer makes it easy work. Place the E6B's speed index under your expected climbing groundspeed on the outer scale. Then find the climb gradient on the inner scale and read the rate of climb required on the outer scale. This method has the advantage of a more exact calculation than is possible with a table.

After converting a few gradients into rates of climb, you'll realize what an impact wind has on an airplane's climb gradient. For once, a headwind is a good thing and a tailwind is bad because the higher the groundspeed, the higher the required rate of climb to comply with a minimum climb gradient.

When the P210 pilot did not fly the ODP for his takeoff airport, he pretty much sealed his family's fate when he departed with a significant tailwind and made a straight-out climb toward rising terrain. The elevation of Morrisville-Stowe is 732 feet msl and the aircraft struck trees at approximately 3,400 feet, which is a gradient of nearly 340 feet per nautical mile. At a groundspeed of 120 knots, a rate of climb better than 700 feet per minute from takeoff would have been required to clear the ridge.

Departure procedures and ATC

Pilots may fly an obstacle departure procedure without specific clearance from air traffic control. In fact, ATC expects that departing pilots will adhere to it unless a controller has issued an alternate departure procedure. Once ATC starts issuing radar vectors or clears the aircraft off the ODP route, ATC takes on responsibility for terrain clearance, but it is assumed that the aircraft will climb at a gradient of at least 200 feet per nautical mile. At 100 knots groundspeed, this equates to a little more than 300 feet per minute.

Don't stop flying the ODP just because you hear the term "radar contact." ATC does not assume terrain clearance responsibilities until controllers actually issue radar vectors or clear the flight off the ODP route. And any ATC-issued heading or clearance off the ODP route may include restrictions to assure terrain clearance, such as, "Leaving 5,000, fly heading 140" or "Out of 3,400, cleared direct Beckley."

Flying a SID on an IFR flight plan requires a specific ATC clearance, but all other departure-procedure pilot responsibilities remain.

If the weather is such that the pilot can see and avoid obstructions, then it is not imperative that he fly the ODP, unless it is part of his ATC clearance.

A pilot departing IFR from an airport without a published instrument approach procedure needs to review a sectional chart before departure because there will be no preplanned ODP for him to consult. Unless obstructions in the airport area can be avoided visually, the pilot will have to make his own crude obstruction analysis from the sectional. In some cases, it may not be safe to depart IFR if visual separation from terrain or obstructions cannot be accomplished. Nearby terrain or obstructions may be the reason there is no instrument approach published.


Bill Kight, AOPA 658477, of Goshen, Kentucky, is a commercial airline pilot.


Use Them VFR

Obstacle departure procedures aren't just for IFR flight. Anytime visual identification of obstructions is difficult — at night or in marginal visibility — adhering to a published ODP is a good idea.

One night in late January 2003, a Piper Aerostar departed Scottsdale, Arizona, for a VFR flight to Santa Fe, New Mexico. The weather was typical Arizona VFR, but there was no moon. After takeoff, the Aerostar made a turn to head directly to Santa Fe.

Unfortunately, McDowell Mountain was five miles from the airport on that heading and the Aerostar struck the mountain just below its summit. Flying the ODP for Scottsdale would have kept the aircraft clear of the terrain the pilot could not see, despite the excellent VFR conditions.

And don't rely on ATC for terrain clearance when flying VFR. In 1999, a Piper Navajo carrying bank paperwork departed North Las Vegas Airport headed for Sacramento, California. Already one hour behind schedule for the planned IFR flight, the pilot elected to depart VFR to avoid a 10-minute ATC delay. After takeoff, the pilot flew a heading suggested by the control tower that would keep the flight clear of the airspace of two different facilities. He continued to fly the heading until striking Gass Peak about 11 miles away. The NTSB said the cause of the accident was the failure of the pilot in command to maintain separation from terrain while operating under VFR.

Pilots wanting to use ODPs have a terrific resource on the AOPA Web site. At AOPA's Airport Directory online ( www.aopa.org/members/airports/), pilots can view and download current NACO charts when they enter the identifier for their departure airport in the U.S. Terminal Procedures search box. That will produce a list of instrument approach procedures and associated data that exist for the airport. If a departure procedure has been developed for the airport, one item in the list of terminal procedures will be Take-Off Minimums. View or download that item, and in its alphabetical listing of cities look for your departure airport under its associated city name. Any departure procedure for the airport will be listed there.

Much of an instrument pilot's flight-planning energy goes into figuring out how to safely descend from the clouds to a runway. Before your next departure in instrument conditions or when flying VFR in marginal conditions or at night, take a few minutes to find out if there is an obstacle departure procedure for your airport so that you can safely get from the runway to cruise altitude. — BK