For those of you who think that flying a SID is safer than flying straight ahead, I hope that you enjoy the following article.
The weather in Las Vegas is 500 feet overcast and 2 miles visibility with rain showers. You are departing via the OVETO NINE SID in an L1011 climb weight limited aircraft. The takeoff briefing is completed with the following statement: “In the event of an engine failure, we will climb to 3175 feet and request radar vectors back to an ILS approach for runway 25R” Ten minutes later you are following down RWY 25R towards V1 and the appropriate call-outs are made, “V1, Rotate.” Just after rotation the number 1 engine fails. You continue climbing towards 3175 feet. Passing through 500 AGL, you advise ATC of the emergency and ask for radar vectors back to land. To your surprise ATC says that they cant supply vectors until you have reached 4000 feet, which is the minimum vectoring altitude (MVA). After some unsuccessful discussion with the controller, you elect to fly the published SID until reaching MVA, since you are certain that it guarantees terrain clearance.
About the time you finish your discussions with ATC, you are passing the 4 DME turn point on the SID and start your turn to a 070° heading. As you roll into the turn you notice that your climb rate is decreasing, you also notice that the radio altimeter is decreasing even though you are still climbing. Halfway through the turn you notice that the radio altimeter is now reading less than 50 feet and continuing to decrease. In seconds you no longer have time to figure out what went wrong.
What went wrong was the SID, and all other procedures based on the United States Standard for Terminal Instrument Procedures (TERPS), only guarantees obstruction clearance when your aircraft can meet the minimum climb rate for the procedure. Lets take a look at what TERPS requires.
TERPS Climb Requirements.
“Based on the aircraft climbing at 200 feet per nautical mile crossing the end of the runway at 35 feet AGL, and climbing to 400 feet above the airport elevation before turning unless specified in the procedure”
TERPS Obstruction Clearance Plane.
“A slope of 152 feet per nautical mile, starting at no higher than 35 feet above the end of the runway is assessed for obstacles. If obstacles penetrate the slope, a climb gradient greater than 200 feet per nautical mile many be added.
From these definitions we can see that TERPS normally requires a minimum climb gradient of 200 feet per nautical mile and that the difference between the climb requirement and the obstruction clearance plane is the operating margin of safety. In the case of OVETO NINE from LAS, the procedure specifies a minimum of 280 feet per nautical mile (700 fpm) to 6000 feet. After your engine failed departing LAS, your aircraft was climbing at 2.7% (3 engine AFM limit) which equates to 163 feet per nautical mile. After entering your turn, your climb gradient was further reduced due to a portion of the lift being vectored into the direction of the turn in order to maintain the aircraft’s bank angle. As you can see your aircraft was climbing at a rate well below the required 280 feet per nautical mile, but worse yet, your aircraft was below the TERPS obstruction plane where obstacles are known to exist. This means that in order for you to be guaranteed adequate obstruction clearance when using an IFR procedure, your aircraft must meet the minimum climb requirements for the procedure, regardless of the number of engines operating. (Note, this article is at least 7 years old, so the OVETO NINE may not exist anymore or may have changed.)
Beamer, do you know how long/far its going to take you to get to 3000 feet? I suggest that you look at the topic about “Takeoff to 1500 feet.”
Flying straight ahead usually gives you a protected track of around 12 miles (AIP type A chart data), in this time, you are expected to decided upon PLAN B.
Mutt.
