Aircraft Performance

Outside air temperature (OAT) 11-4 )teef( edutitla ytisneD as air density decreases (higher density altitude), aircraft flight level. Density altitude can also be determined by referring performance decreases. A decrease in air density means a to the table and chart in Figures 11-3 and 11-4 respectively. high density altitude; an increase in air density means a lower density altitude. Density altitude is used in calculating aircraft Effects of Pressure on Density performance. Under standard atmospheric condition, air at Since air is a gas, it can be compressed or expanded. When each level in the atmosphere has a specific density; under air is compressed, a greater amount of air can occupy a standard conditions, pressure altitude and density altitude given volume. Conversely, when pressure on a given volume identify the same level. Density altitude, then, is the vertical of air is decreased, the air expands and occupies a greater distance above sea level in the standard atmosphere at which space. That is, the original column of air at a lower pressure a given density is to be found. Density altitude is computed using pressure altitude and 15,000 temperature. Since aircraft performance data at any level is 14,000 based upon air density under standard day conditions, such performance data apply to air density levels that may not be 14,000 13,000 identical to altimeter indications. Under conditions higher o d r ir e lo c w tly e r f r t o h m an t h st e a n al d t a im rd e , t e th r. ese levels cannot be determined 13,000 12,000 et) e D a te l m t e i n t p u s e d it r e y a t a u a n r l e d ti t v u th a d e r e i n a i t c s io o d n rr s e e . t c e S t r i m i n n g c in e t e h d d i e s b n a y s l i t t f i y t i u r v s d t a e r f i f i e n o s d r d i n n i o r g e n c p s t t l r a y e n s d w s a u i r r t d h e 1 1 2 1 , , 0 0 0 0 0 0 11,0 1 0 0 0 ,0 00 e s s ur e altit u d e (f p al r t e it s u s d u e re m , a a y n d e x i i n s v t e fo rs r e a l y w i w de it h ra n te g m e p o e f r t a e t m ur p e e , r a a t u g r i e v e b n y a p l r l e o s w su in r g e 10,000 S ta n 9,000 Pr the density to vary. However, a known density occurs for d a a n ir y , o o f n c e o t u em rse p , e h ra a t s u a re p a ro n n d o p u r n es c s e u d r e e f a f l e t c it t u o d n e . a T ir h c e ra d f e t n an si d ty e o n f g i t n h e e 9,000 a r d te m 8,000 performance. Regardless of the actual altitude at which 8,000 p e the aircraft is operating, it will perform as though it were r a tu 7,000 r operating at an altitude equal to the existing density altitude. 7,000 e 6,000 For example, when set at 29.92 "Hg, the altimeter may 6,000 indicate a pressure altitude of 5,000 feet. According to the 5,000 AFM/POH, the ground run on takeoff may require a distance 5,000 o if f t 7 h 9 e 0 t e f m ee p t e u r n a d tu e r r e s t i a s n 2 d 0 a r ° d C t e a m bo p v e e r a s t t u a r n e d c a o rd n , d t i h ti e o n e s x . p H an o s w io e n v e o r f , 4,000 a fr i o r m ra i t s a e b s l e th s e o d r e g n ra si p t h y s l , e o v r e b l. y U d s e in ri g v i t n e g m t p h e e r a d t e u n r s e i t c y o a rr l e ti c tu ti d o e n w da it t h a 4,000 3,000 a computer, it may be found that the density level is above 3,000 7,000 feet, and the ground run may be closer to 1,000 feet. 2,000 2,000 Air density is affected by changes in altitude, temperature, 1,000 el and humidity. High density altitude refers to thin air while e v 1,000 a l low density altitude refers to dense air. The conditions that e result in a high density altitude are high elevations, low S -1,000 -2,000 atmospheric pressures, high temperatures, high humidity, or Sea level C -20° -10° 0° 10° 20° 30° 40° some combination of these factors. Lower elevations, high atmospheric pressure, low temperatures, and low humidity F 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100° are more indicative of low density altitude. Using a flight computer, density altitude can be computed by Figure 11-4. Density altitude chart. inputting the pressure altitude and outside air temperature at