# How far from the runway should a small plane start its descent from 5000ft?

I don't fly, don't have a clue. But one of the main characters in my book DOES: it's a Cessna 152, just him at 14 stone and a couple of small bags, all conditions are perfect and he's flown from about 140 NM away. Would 5000ft be about the right altitude?

The question is: how far away is the runway (a grass one on an unlicensed airfield) when he starts his descent? It's a direct approach, no pattern.

• Have a look at this question/answer. It should be enough to get you in an acceptable range. – Dan Priest Mar 8 '17 at 21:30
• Also, regarding altitude, see this question, it would depend on the direction of flight and if they are VFR or IFR. – Ron Beyer Mar 8 '17 at 21:33
• I applaud you for asking. I've been reading the Dirk Pitt novels by Clive Cussler, and his descriptions of flying have a tenuous grasp on reality, based on what I've learned here, and it's rather distracting. – FreeMan Mar 9 '17 at 15:07
• Regarding whether the cruising altitude is appropriate, assuming he's flying VFR (Visual Flight Rules), he should be at an odd thousand plus 500 ft for east headings (360-179 degrees) or an even thousand plus 500 ft for west headings (180-359 degrees). Also, you didn't specify a field elevation. – Fred Larson Mar 9 '17 at 17:32

For a comfortable decent you generally want to come down at 500 Ft/Min on the Vertical speed indicator. The 152 is doing about 95Kts over the ground (assuming no wind). So you are covering about 1.5 miles a minute to round it off. So you need to drop 5000 ft on your approach to the area. At a comfortable rate that will take about 10 minutes. In that time, covering 1.5 miles a minute, you will need to start your decent about 15 nautical miles out.

• While this method of calculation does apply towards answering this question, your answer does not. The question specifies a straight in approach with no pattern flown, thus the descent is to be made to the field elevation. A more correct answer would be about 15 NM, which is true either for a 3° descent path, or for your calculation method. – J Walters Mar 9 '17 at 4:26
• I must have overlooked that last sentence. I have corrected as such. – Dave Mar 9 '17 at 13:26
• Thank you guys SOO much! I've used the advice and finally got the character down realistically. His next flight to same airfield is in hot summer months and it's on the east coast so maybe he'll come in from over the sea to avoid thermals from land. Realistic scenario for experienced pilot? Thanks again, you've been quick and really helpful. – Nathan K Strawn Mar 11 '17 at 14:02
• @NathanKStrawn that really depends on the airport but generally speaking you can come in from over water. However you are limited as to how far out over the water you can fly here in the US due to the ADIZ which you dont really cross unless you are leaving the country. – Dave Mar 11 '17 at 17:23
• @NathanKStrawn However most pilots generally avoid flying over open water if they can help it. There is no reason, and perhaps an increased risk to go out over water if you can get to where you need to be over land only. – Dave Mar 11 '17 at 17:25

The standard 3° glide path works out to roughly 3nm per 1000ft. This is very easy to calculate in the air, regardless of airspeed.

Assuming your character’s destination is at sea level, or close enough that it doesn’t matter, he has to descend the entire 5000ft, which gives us 15nm.

If he is going to enter the traffic pattern (which is probably safer), he will want to arrive at the airport 1000ft above the ground, which means only 4000ft to descend, and 12nm.

If the airport isn’t near sea level, make the appropriate adjustments. For instance, if he’s flying to Denver, he would need to climb to reach the airport because at a mere 5000ft, he’s underground!

Regarding your follow-up comment about flying over water, pilots of single-engine piston planes usually remain within gliding distance of land for safety reasons, which will typically be about 1.5nm per 1000ft of altitude (or half the standard descent distance).

Typical decent(not including aerobatics and such) is a 3-6 degree slope regardless of aircraft, this is 300-650 feet per nautical mile. 5000feet above touchdown elevation thus yields 7.7 to 16.7NM

Power off glide distance for a C152 from 5000 with no wind would be about 6.5 NM, they have approx 8:1 glide ratio.

The weight of the aircraft will effect optimal speed, but their will be no significant effect on the decent angle or distance.

5000 feet above ground is generally reasonable for a C152. Service ceiling is about 14700 above sea level. (they are flying at 5000 feet plus the airport elevation. If the airport is 1500 feet above sea level then the airplane is cruising at 6,500 above sea level)