Climb Gradient Question

[heywatchthis]

I know, I know everyone is sick of this. And yes I did do a search and found tons of info previously discussed.

Background?

An obstacle-free departure flight path is based on your aircraft climbing at least 200 feet per nautical mile, after it crosses the end of the runway at least 35 feet above the ground. In addition, you must be able to climb to 400 feet above the airport elevation within 2 nautical miles, before reaching a point where a turn is required. (IE 200 FPNM)

ALSO?

A slope of 152 feet per nautical mile is assessed for obstacles. If no obstacle penetrates this slope, the 200 feet per nautical mile climb gradient provides you with a minimum of 48 feet of obstacle clearance for each mile of flight. If obstacles do penetrate this slope, special avoidance procedures such as ceiling and visibility minimums, detailed flight maneuvers, and/or greater climb gradients are specified.

QUESTION?

If there is an obstacle just under the 152 fpnm (say 150 fpnm), then you will have no indication of an obstacle and it is considered an obstacle free departure flight path.
BUT in order to make the standard 200 fpnm requirement to 400 ft, you would need a climb gradient of 3.29%. (200 / 6076 *100)

If you take off at a weight that gives you the minimum climb gradient for 2nd segment climb of 2.4% gross, and a 1.6% net, seeing how you know of no obstacles...
YOU WILL NOT BE ANYWHERE NEAR 3.3% AND COULD HIT THE OBSTACLE.

So why the heck do we need to make a minimum 2.4 % climb, when obstacles are assessed up to 3.3% climb gradient with no warning?

 

[guido411]

This is why a 3.3% gradient is required to depart IFR (below 1000-3) in a Part 25 airplane. The 1.6% gradient is for VFR departures which should allow you the ablity to see and avoid the obstacle.

 

[heywatchthis]

This is why a 3.3% gradient is required to depart IFR (below 1000-3) in a Part 25 airplane. The 1.6% gradient is for VFR departures which should allow you the ablity to see and avoid the obstacle.

OK, good answer! Where does part 25 state VFR Versus IFR departures?

 

[Doc Holiday]

It doesn't. Part 25 only specifies what is required for certification of aircraft. Minimum climb gradients are included in this, but they are not related in any way to instrument procedures.

121.189(d) or 135.379(d) tells you what minimum obstacle clearance needs to be for the net takeoff flight path (35 ft above and 200 feet horizontally, etc. etc)

121.651 and 91.175 say that operators for hire cannot takeoff with weather less than that prescribed in Part 97 (your DPs and ODPs). If no climb gradients are published in a DP or ODP, then 200 ft/nm (3.3%) is required. AIM 5-2-7

The 1.6% net (2.4% gross) mentioned above is the absolute minimum 2nd segment climb gradient allowed. Taking off at a weight higher than would allow that gradient in case of an engine failure (2 engine airplane) would be exceeding an AFM limitaion.

 

[Wantfrys]

but were does it actual say "in case of engine failure"

 

[ttflyer]

The point of all these numbers is that you have to assume you are going to lose it, and still be able to meet the minimum performance requirements to clear obstacales.

 

[LJ45]

Lead sled....Help us! LOL

 

[gunfyter]

but were does it actual say "in case of engine failure"

It says it in part 135. Under 91 there is no requirement to make the TERPS climb gradient in the event of an engine failure....

 

[ttflyer]

It says it in part 135. Under 91 there is no requirement to make the TERPS climb gradient in the event of an engine failure....

Agreed. But the FAA can still violate you (part 91) under the careless and reckless catch all. Like most of 91, you would probably have to crash to get their attention...

If I can't meet the TERPS IFR, I depart VFR (if I can safely do so). If I can't depart VFR, I don't go...

 

[Wantfrys]

It says it in part 135. Under 91 there is no requirement to make the TERPS climb gradient in the event of an engine failure....

Ok first were in 135 I have got into heated talks with guys at Flight Safety about this. Also I know there is a difference with Part 25 ,27 but are you telling me that a PC-12(Single engine) would never be able to departe under IFR under P-135?