Page 66 - AFMAN 15-111, 12 MAR 2019

66 AFMAN15-111 12 MARCH 2019

13.4.3. Additional derived pressure-related reports are added to observations when occurring
and/or at regular intervals in accordance with this manual, higher headquarters guidance, and
local procedures. These reports include but are not limited the following:
13.4.3.1. Sea-level Pressure (SLP) is a report of the theoretical reduction of station
pressure to sea level. Where the earth’s surface is above sea level, it is assumed the
atmosphere extends to sea level below the observing location and the properties of the
hypothetical atmosphere are related to conditions observed at the unit. Note: SLP may be
referred to by the acronym “QFF” by the international community.
13.4.3.2. Pressure tendency is a coded report (5-group) included on the 3-hourly
observations that indicates the characteristic and amount of pressure change during the 3-
hour period preceding the observation.
13.4.3.3. Pressure falling rapidly (PRESFR) and pressure rising rapidly (PRESRR) are
remarks used to indicate a rapid fluctuation in pressure has occurred. These remarks are
reported in column 13 whenever the station pressure changes at a rate of at least 0.06 iHg
per hour (0.01 iHg per 10 minutes) with a change of at least 0.02 iHg having occurred at
the time of observation.

13.4.3.4. Pressure Altitude (PA) is an altitude in the standard atmosphere at which a given
pressure is observed. It is the indicated altitude above or below the 29.92 iHg constant-
pressure surface. Note: PA may be referred to by the acronym “QNE” by the international
community.

13.4.3.5. Density Altitude (DA) is the PA corrected for virtual temperature deviations
from the standard atmosphere.

13.4.3.6. Field Elevation (Ha) is the officially designated elevation of an airfield/site above
mean sea level. It is the elevation of the highest point on any of the runways of the
airfield/site.

13.4.3.7. Station Elevation (Hp) is the officially designated height above sea level to which
station pressure pertains; generally, the same as field elevation.

Table 13.1. Units of Measure and Resolution of Pressure Parameters.
Parameter Unit of Measure Resolution
Station Pressure Inches of Mercury 0.005 iHg
Altimeter Setting Inches of Mercury 0.01 iHg
Sea Level Pressure Hectopascals 0.1 hPa
Pressure Altitude Feet 10 ft
Density Altitude Feet 10 ft

13.5. Manual Observing Methods. All organizations with a permanent weather observing
mission in direct support of flying operations will have a primary pressure measurement instrument
and will designate a back-up pressure measuring instrument. (T-1). The primary method to obtain
pressure measurements are by directly reading the sensor output from an FBWOS or its associated
software (i.e. JET).