The basic needs of the learner must be satisfied before he or
she is ready or capable of learning (see Chapter 1, Human
Behavior). The instructor can do little to motivate the learner
if these needs have not been met. This means the learner must
want to learn the task being presented and must possess the
requisite knowledge and skill. In SBT, the instructor attempts
to make the task as meaningful as possible and to keep it
within the learner’s capabilities.
Students best acquire new knowledge when they see a clear
reason for doing so, often show a strong interest in learning
what they believe they need to know next, and tend to set
aside things for which they see no immediate need. For
example, beginning flight students commonly ignore the
flight instructor’s suggestion to use the trim control. These
students believe the control yoke is an adequate way to
manipulate the aircraft’s control surfaces. Later in training,
when they must divert their attention away from the controls
to other tasks, they realize the importance of trim.
Instructors can take two steps to keep their students in a state
of readiness to learn. First, instructors should communicate a
clear set of learning objectives to the student and relate each new topic to those objectives. Second, instructors should
introduce topics in a logical order and leave students with a
need to learn the next topic. The development and use of a
well-designed curriculum accomplish this goal.
Readiness to learn also involves what is called the “teachable
moment” or a moment of educational opportunity when a
person is particularly responsive to being taught something.
One of the most important skills to develop as an instructor
is the ability to recognize and capitalize on “teachable
moments” in aviation training. An instructor can find or
create teachable moments in flight training activity: pattern
work, air work in the local practice area, cross-country, flight
review, or instrument proficiency check.
Teachable moments present opportunities to convey
information in a way that is relevant, effective, and memorable
to the student. They occur when a learner can clearly see how
specific information or skills can be used in the real world.
For example, while on final approach several deer cross the
runway. Bill capitalizes on this teachable moment to stress the
importance of always being ready to perform a go-around.
All learning involves the formation of connections and
connections are strengthened or weakened according to
the law of effect. Responses to a situation that are followed
by satisfaction are strengthened; responses followed by
discomfort are weakened, either strengthening or weakening
the connection of learning. Thus, learning is strengthened
when accompanied by a pleasant or satisfying feeling, and
weakened when associated with an unpleasant feeling.
Experiences that produce feelings of defeat, frustration,
anger, confusion, or futility are unpleasant for the student.
For example, if Bill teaches landings to Beverly during the
first flight, she is likely to feel inferior and be frustrated,
which weakens the learning connection.
The learner needs to have success in order to have more
success in the future. It is important for the instructor to create
situations designed to promote success. Positive training
experiences are more apt to lead to success and motivate the
learner, while negative training experiences might stimulate
forgetfulness or avoidance. When presented correctly, SBT
provides immediate positive experiences in terms of real
To keep learning pleasant and to maintain student motivation,
an instructor should make positive comments about the
student’s progress before discussing areas that need
improving. Flight instructors have an opportunity to do this
during the flight debriefing. For example, Bill praises Beverly on her aircraft control during all phases of flight, but offers
constructive comments on how to better maintain the runway
centerline during landings.
Connections are strengthened with practice and weakened
when practice is discontinued, which reflects the adage “use
it or lose it.” The learner needs to practice what has been
learned in order to understand and remember the learning.
Practice strengthens the learning connection; disuse weakens
it. Exercise is most meaningful and effective when a skill is
learned within the context of a real world application.
Primacy, the state of being first, often creates a strong, almost
unshakable impression and underlies the reason an instructor
must teach correctly the first time and the student must learn
correctly the first time. For example, a maintenance student
learns a faulty riveting technique. Now the instructor must
correct the bad habit and reteach the correct technique.
Relearning is more difficult than initial learning.
Also, if the task is learned in isolation, it is not initially
applied to the overall performance, or if it must be relearned,
the process can be confusing and time consuming. The
first experience should be positive, functional, and lay the
foundation for all that is to follow.
Immediate, exciting, or dramatic learning connected to
a real situation teaches a learner more than a routine or
boring experience. Real world applications (scenarios)
that integrate procedures and tasks the learner is capable
of learning make a vivid impression and he or she is least
likely to forget the experience. For example, using realistic
scenarios has been shown to be effective in the development
of proficiency in flight maneuvers, tasks, and single-pilot
resource management (SRM) skills.
The principle of recency states that things most recently
learned are best remembered. Conversely, the further a
learner is removed in time from a new fact or understanding,
the more difficult it is to remember. For example, it is easy for
a learner to recall a torque value used a few minutes earlier,
but it is more difficult or even impossible to remember an
unfamiliar one used a week earlier.
Memorial Day endures as a holiday which most businesses observe because it marks the unofficial beginning of summer. The Veterans of Foreign Wars (VFW) and Sons of Union Veterans of the Civil War (SUVCW) advocated returning to the original date, although the significance of the date is tenuous. The VFW stated in 2002:
In 2000, Congress passed the National Moment of Remembrance Act, asking people to stop and remember at 3:00 PM.
On Memorial Day, the flag of the United States is raised briskly to the top of the staff and then solemnly lowered to the half-staff position, where it remains only until noon. It is then raised to full-staff for the remainder of the day.
The National Memorial Day Concert takes place on the west lawn of the United States Capitol. The concert is broadcast on PBS and NPR. Music is performed, and respect is paid to the men and women who gave their lives for their country.
Across the United States, the central event is attending one of the thousands of parades held on Memorial Day in large and small cities. Most of these feature marching bands and an overall military theme with the Active Duty, Reserve, National Guard and Veteran service members participating along with military vehicles from various wars.
During World War II, more airmen died in combat than Marines.
Operation Tidal Wave was an air attack by bombers of the United States Army Air Forces (USAAF) based in Libya and Southern Italy on nine oil refineries around Ploiești, Romania on 1 August 1943, during World War II. It was a strategic bombing mission and part of the "oil campaign" to deny petroleum-based fuel to the Axis. The mission resulted in "no curtailment of overall product output."
This mission was one of the costliest for the USAAF in the European Theater, with 53 aircraft and 660 air crewmen lost. It was proportionally the most costly major Allied air raid of the war and its date was later referred to as "Black Sunday". Five Medals of Honor and 56 Distinguished Service Crosses along with numerous others awards were awarded to Operation Tidal Wave crew members.
Here is the story of John C. Waldron:
June 4, 1942. The 15 Douglas TBD-1 Devastators of VT-8 launched from Hornet's flight deck in search of the enemy. Before takeoff, LCDR Waldron had a dispute with the Hornet's Commander, Air Group, Stanhope C. Ring, and Hornet CO Marc Mitscher about where the Japanese carriers would be found. Despite having a contact report showing the Japanese southwest of Hornet, Mitscher and Ring ordered the flight to take a course due west, in the hopes of spotting a possible trailing group of carriers. Waldron argued for a course based on the contact report, but was overruled. Once in the air, Waldron attempted to take control of the Hornet strike group by radio. Failing that, he soon split his squadron off and led his unit directly to the Japanese carrier group. Waldron, leading the first carrier planes to approach the Japanese carriers (somewhat after 9:00AM local time, over an hour before the American dive bombers would arrive), was grimly aware of the lack of fighter protection, but true to his plan of attack committed Torpedo 8 to battle. Without fighter escort, underpowered, with limited defensive armament, and forced by the unreliability of their own torpedoes to fly low and slow directly at their targets, the Hornet torpedo planes received the undivided attention of the enemy's combat air patrol of Mitsubishi Zero fighters. All 15 planes were shot down. Of the 30 men who set out that morning, only one—Ensign George H. Gay, Jr., USNR—survived. Their sacrifice, however, had not been in vain. Torpedo 8 had forced the Japanese carriers to maneuver radically, delaying the launching of the planned strike against the American carriers. After further separate attacks by the remaining two torpedo squadrons over the next hour, Japanese fighter cover and air defense coordination had become focused on low-altitude defense. This left the Japanese carriers exposed to the late-arriving SBD Dauntless dive bombers from Yorktown and Enterprise, which attacked from high altitude. The dive bombers fatally damaged three of the four Japanese carriers, changing the course of the battle.
The document that specifies the requirements of a Flight Review is AC 61-98B. From 61-98B:
Under § 61.56(c) no person may act as PIC of an aircraft unless within the preceding 24 calendar-months that person has accomplished a satisfactory flight review in an aircraft for which that pilot is appropriately rated. An appropriately-rated instructor or other designated person must conduct the flight review. The purpose of the flight review is to provide for a regular evaluation of pilot skills and aeronautical
Pilots and CFIs should be aware that, under § 61.56(d), there is no requirement for pilots who have completed certain proficiency checks and ratings within the preceding 24 calendar-months to accomplish a separate flight review. These accomplishments include satisfactory completion of pilot proficiency checks conducted by the FAA, an approved pilot check airman, a Designated Pilot Examiner (DPE), or a U.S. Armed Force for a pilot certificate, rating, or operating privilege. However, the FAA recommends that pilots consider also accomplishing a review under some of the following circumstances. For example, a pilot with an Airplane Single-Engine Land (ASEL) rating may have recently obtained a glider rating, but may still wish to consider obtaining a flight review in a single-engine airplane if the appropriate 24-month period has nearly expired.
Review of Maneuvers and Procedures:
(1) The maneuvers and procedures covered during the review are those which, in the opinion of the CFI conducting the review, are necessary for the pilot to perform in order to demonstrate that he or she can safely exercise the privileges of his or her pilot certificate.
Accordingly, the CFI should evaluate the pilot’s skills and knowledge to the extent necessary to ensure that he or she can safely operate within regulatory requirements throughout a wide range of conditions. The CFI should always include abnormal and emergency procedures applicable to
the aircraft flown in the flight review.
(2) The CFI may wish to prepare a preliminary plan for the flight review based on an interview or other assessment of the pilot’s qualifications and skills. The CFI should outline a sequence of maneuvers to the pilot taking the review. For example, this may include a cross-country flight to another airport with maneuvers accomplished while en route. It could also include a period of simulated instrument flight time. The CFI should request that the pilot conduct whatever preflight preparation is necessary to complete the planned flight. This preparation should include all items required in part 91, § 91.103, such as checking weather, calculating required runway lengths, calculating Weight and Balance (W&B), completing a flight log, filing a flight plan, and conducting the preflight inspection.
(3) Before beginning the flight portion of the review, the CFI should discuss various operational areas with the pilot. This oral review should include, but not be limited to, areas such as aircraft systems, speeds, performance, meteorological and other hazards (e.g., windshear and wake turbulence), operations in controlled airspace, and abnormal and emergency procedures.
The emphasis during this discussion should be on practical knowledge of recommended procedures and regulatory requirements.
(4) Regardless of the pilot’s experience, the CFI may wish to review at least those maneuvers considered critical to safe flight, such as stalls, slow flight, and takeoffs and landings. Based on his or her in-flight assessment of the pilot’s skills, the CFI may wish to add other maneuvers from the PTS appropriate to the pilot’s grade of certificate. All reviews should include those areas within the PTS identified as “Special Emphasis.” Appendix 5 includes a list of suggested maneuvers. The FAA does not intend this list to be all-inclusive, nor does it limit a CFI’s discretion in selecting other appropriate maneuvers and procedures. To the greatest possible extent, the CFI should organize and sequence the selected maneuvers in a realistic
scenario appropriate to the kind of flying normally done by the pilot.
(5) The role of the CFI during the review is to provide an evaluation. However, the instructor is not limited to this role and may provide specific instruction to an airman on any areas the instructor notes as being weak. This additional instruction does not preclude the pilot’s successful completion of the review as long as the deficiencies are corrected. If the additional instruction does not correct the deficiencies, and/or it becomes apparent to the instructor that additional flights will be necessary, the CFI should discuss the situation with the pilot and proceed accordingly.
Gregory Poole is a former Coast Guard flight engineer, based in Southern California. When he was a teenager, he saw a poster of a military helicopter, and that was his inspiration to enlist.
His training was in North Carolina, learning avionics, electrical, mechanical and rescue. He cross-trained in numerous fields.
As an early flight engineer, he performed a rescue at the bottom of a cliff where a car had gone off the road, and he had to conduct the rescue with the rotor blades inches from the face of the cliff. His rescue helicopter was the HH-52, similar to the Sea King helicopter.
As flight engineer, he performed all preflight and post-flight inspections, with special attention to hydraulics. During actual missions, he operated the night spotlight and forward-looking infra-red (FLIR), which was essential in night rescue missions.
Greg also participated in law enforcement missions.
Greg is also an experienced martial artist instructor. He started in Philippines martial arts, then branched in to aikido, tae kwan do, hapkido, jeet kun do and salat. He has developed his own system, and now trains youngsters.
In May of last year I was accepted into the Writers Guild Foundation Veterans Writing Project. The program accepts 50 veterans each year (I was turned down the previous year) and holds a 3-day Retreat to launch the year's activities.
We were divided into groups of about 8 veterans and paired with working screen writing professionals to brainstorm our topics and refine our writing process. Then we were mentored throughout the year by more professional writers, with meetings twice each month. those of us who did not live in the Los Angeles area were able to participate via Facebook video and telephone conferences.
I based my script on my Hamfist novel series. I quickly discovered that a screenplay is totally different from a novel, and my script evolved dramatically, mostly due to the feedback of my mentor, Sabrina Almeida. With her help and guidance, my script went from not-ready-for-prime-time to pretty darned good.
And now the yearlong program, for me, is over, and I was invited to "pitch" my script to industry heavyweights. So, two days ago, I went to Los Angeles for the pitch-fest.
Here’s the pitch:
I'm Major George Nolly of the US Air Force
Author of the Hamfist Novel Series, with multiple Best-sellers that have been ranked #1 Fiction in the Vietnam War - History category with over 151,000 units downloaded and paperback sales on Amazon.
I teach Aviation at Metro State University, and I'm a Flight Instructor at United Airlines, where I flew for 26 years after active duty.
I have two masters, and a doctorate in Homeland Security, but before that, I was a cadet at the US Air Force Academy because I wanted to be a pilot, just like my father.
I did two tours in Vietnam with 198 combat missions flying an F-4 fighter jet, and let me tell you, there is nothing in this world that compares to being strapped to two J79 engines pushing 36,000 foot pounds of thrust at Mach 1 while a SAM is closing in on your ass.
It was everything I hoped for and more.
But before I got into my first dogfight, I had to get through my first combat tour.
After pilot training, I went over as a FAC, a Forward Air Controller, in an O-2, which was a tiny, twin-prop Cessna used to fly low to the ground, and spot high-value targets in enemy territory.
It was NOT what I signed up for.
He's sent to Vietnam in an O-2, one of the slowest planes in the service, where he meets SPEEDBRAKE, fellow pilot and mentor, who shows him what a FAC really does:
He loiters in the area long enough to direct fighters in for an air strike. The way you do this is at night is by GOING CHRISTMAS TREE, where we would turn on all our exterior lights and light up like a christmas tree to attract enemy ground fire, so that Charlie would reveal himself to our fighters for an air strike.
It's on a close call going Christmas Tree where our hero earns the call sign HAMFIST.
When the Base Commander offers winner's choice of aircraft for the pilot with the highest kill ratio, Hamfist sees a way into an F-4, that is, if he can beat his nemesis, Tank, the squadron Top Dog.
However, Hamfist's relentless pursuit leads him to fly fast and loose. When his flying puts others in jeopardy, he is deemed reckless, and sent on mandatory R&R.
While on R&R in Tokyo, he meets SAMANTHA - SAM, a recent Harvard Law Grad. Samantha has just signed up to join the Air Force as a JAG, and has a thing for fighter pilots. For the first time, Hamfist has dreams of something big in his life, other than flying fast.
That dream is interrupted when Hamfist gets word that his Mentor SPEEDBRAKE is shot down, and Hamfist must return to Vietnam to pack up Speedbrake's things for his family.
On his first mission back, distracted by how he left things with Sam, Hamfist gets shot down over the trail, and injured during his rescue.
After he's patched up, he persuades the doc to clear him to fly, even though the full extent of his injuries are not yet known.
The deadline arrives for the competition, and he has just enough time for one more sortie to secure his lead over TANK.
However, when as he enters the target area, he hears a distress call from a downed F-4. Hamfist forfeits his target to rescue the pilot.
Hamfist returns to base as a hero, however, he loses the competition to Tank, and along with that, his dreams of piloting an F-4.
A medical exam reveals that his injuries were more severe than previously thought, and he also loses his Air Force Flight Clearance.
Hamfist is overcome by the failure in his pursuit to follow in his father's footsteps.
Unable to turn to Sam, for fear that her affections will change, now that he will never be a fighter pilot, he severs his relationship with her while she is still in Officer Training.
Hamfist is given the option to leave the service at the end of his tour with an Honorable Discharge, or remain grounded for the rest of his career.
When word of his heroism reaches the private sector, however, Hamfist is offered a job as a civilian test pilot... in an F-4.
Assigned as the Interim Squadron Intel Officer until a replacement arrives, he witnesses the dedication of the men left behind on base while pilots flew their combat missions.
- The maintenance crews that perform 20 man-hours to every one hour he was in the air.
He sees how each person's contribution to the war effort is critical.
Hamfist understands that the War Effort comes before his personal desires, and extends his tour in Vietnam as a Ground officer.
That's when his replacement Intel Officer arrives on base, and Hamilton walks in to brief... Samantha, freshly graduated from Intel School.
Tom Cappelletti wanted to be a pilot ever since he was a child, but his first Air Force assignment was as an engineer. Yom spent three years at Wright-Patterson Air Force Base as a Test Program Manager before getting an assignment to Undergraduate Pilot Training in the Reserves.
After earning his wings, Tom flew the C-9 aeromedical evacuation aircraft, flying patients and their families to medical facilities all over the united States. He has landed virtually everywhere that has 5000 feet of concrete in the aeromedical evacuation role.
Tom participated in the commissioning of a painting of the C-9 to hang at Scott Air Force Base to commemorate the aircraft.
Tom became an airline pilot with a major carrier, and now flies the B737NG. His routes include Hawaii, Canada, and South America. Like every other pilot at his airline tom is ETOPS (Extended Twin Engine Operations) qualified.
Tom has an eclectic collection of aviation memorabilia, books and prints, and has had many of the items personally signed.
Normalization of deviance is a term first coined by sociologist Diane Vaughan when reviewing the Challenger disaster. Vaughan noted that the root cause of the Challenger disaster was related to the repeated choice of NASA officials to fly the space shuttle despite a dangerous design flaw with the O-rings. Vaughan describes this phenomenon as occurring when people within an organization become so insensitive to deviant practice that it no longer feels wrong. Insensitivity occurs insidiously and sometimes over years because disaster does not happen until other critical factors line up. In clinical practice, failing to do time outs before procedures, shutting off alarms, and breaches of infection control are deviances from evidence-based practice. As in other industries, health care workers do not make these choices intending to set into motion a cascade toward disaster and harm. Deviation occurs because of barriers to using the correct process or drivers such as time, cost, and peer pressure. As in other industries, operators will often adamantly defend their actions as necessary and justified. Although many other high-risk industries have embraced the normalization of deviance concept, it is relatively new to health care. It is urgent that we explore the impact of this concept on patient harm. We can borrow this concept from other industries and also the steps these other high-risk organizations have found to prevent it.
In September 2016, Capt. David Whitson (United) was diagnosed with acute myeloid leukemia, a condition in which white blood cells that manage the body’s immune system form abnormally. The then B-787 first officer was treated at the Texas Oncology–Baylor Charles A. Sammons Cancer Center in Dallas, Tex., where he spent an initial 30 days undergoing tests and chemotherapy.
“I had a mutation called FLT3 that put me at high risk for not reaching remission and also in a high-incidence category for relapse even if remission was achieved,” he recalled, adding, “My best shot was to have a bone marrow transplant, also called a stem cell transplant. Without it, I had a 5 percent chance of survival.”
Whitson was released from the hospital for a brief break. During this period, doctors conducted a bone marrow biopsy and discovered that the pilot’s cancer was in remission, a condition necessary to achieve before a bone marrow transplant could be conducted. Whitson and his doctors quickly found a donor.
“It was hard for me to wrap my head around the fact that a complete stranger would be willing to give me bone marrow stem cells and potentially save my life,” he acknowledged. Whitson endured additional rounds of chemotherapy and a full-body radiation scan to ensure his body was ready and on Dec. 21, 2016, received the transplant. Within several days, his new immune system was up and running.
Thirteen days after the transplant, Whitson was released from the hospital. He noted that prior to the transfusion of stem cells his blood type was B+, but today it’s O-. In addition, the DNA in his blood is different from that in his body.
Whitson encourages everyone to donate blood. “I needed more than a dozen blood and platelet transfusions during my treatments,” he said. The United pilot also urges those interested to join the national bone marrow registry at bethematch.org or www.dkms.org. “There’s a lack of diversity within the registry, and minorities are greatly needed,” he shared.
“Every day is a gift,” Whitson remarked, who credits ALPA’s Aeromedical Office for advising him and helping him jump through the necessary hoops to acquire his special issuance medical certificate and return to the cockpit. He also gave a nod to his medical benefits, noting, “I was on long-term disability for more than two years, and my medical insurance was excellent. Thank you, ALPA!”
The stability of the atmosphere depends on its ability to
resist vertical motion. A stable atmosphere makes vertical
movement difficult, and small vertical disturbances dampen
out and disappear. In an unstable atmosphere, small vertical air
movements tend to become larger, resulting in turbulent airflow
and convective activity. Instability can lead to significant
turbulence, extensive vertical clouds, and severe weather.
Rising air expands and cools due to the decrease in air
pressure as altitude increases. The opposite is true of
descending air; as atmospheric pressure increases, the
temperature of descending air increases as it is compressed.
Adiabatic heating and adiabatic cooling are terms used to
describe this temperature change.
The adiabatic process takes place in all upward and
downward moving air. When air rises into an area of lower
pressure, it expands to a larger volume. As the molecules
of air expand, the temperature of the air lowers. As a result,
when a parcel of air rises, pressure decreases, volume
increases, and temperature decreases. When air descends,
the opposite is true. The rate at which temperature decreases
with an increase in altitude is referred to as its lapse rate.
As air ascends through the atmosphere, the average rate of
temperature change is 2 °C (3.5 °F) per 1,000 feet.
Since water vapor is lighter than air, moisture decreases air
density, causing it to rise. Conversely, as moisture decreases,
air becomes denser and tends to sink. Since moist air cools
at a slower rate, it is generally less stable than dry air since
the moist air must rise higher before its temperature cools
to that of the surrounding air. The dry adiabatic lapse rate
(unsaturated air) is 3 °C (5.4 °F) per 1,000 feet. The moist
adiabatic lapse rate varies from 1.1 °C to 2.8 °C (2 °F to
5 °F) per 1,000 feet.
The combination of moisture and temperature determine the
stability of the air and the resulting weather. Cool, dry air
is very stable and resists vertical movement, which leads to
good and generally clear weather. The greatest instability
occurs when the air is moist and warm, as it is in the tropical
regions in the summer. Typically, thunderstorms appear on
a daily basis in these regions due to the instability of the
As air rises and expands in the atmosphere, the temperature
decreases. There is an atmospheric anomaly that can occur;
however, that changes this typical pattern of atmospheric
behavior. When the temperature of the air rises with altitude, a
temperature inversion exists. Inversion layers are commonly
shallow layers of smooth, stable air close to the ground. The
temperature of the air increases with altitude to a certain
point, which is the top of the inversion. The air at the top
of the layer acts as a lid, keeping weather and pollutants
trapped below. If the relative humidity of the air is high, it
can contribute to the formation of clouds, fog, haze, or smoke
resulting in diminished visibility in the inversion layer.
Surface-based temperature inversions occur on clear, cool
nights when the air close to the ground is cooled by the
lowering temperature of the ground. The air within a few
hundred feet of the surface becomes cooler than the air above
it. Frontal inversions occur when warm air spreads over a
layer of cooler air, or cooler air is forced under a layer of
From AC 006B:
Vertical Motion Effects on an Unsaturated Air Parcel. As a bubble or parcel of air ascends (rises), it moves into an area of lower pressure (pressure decreases with height). As this occurs, the parcel expands. This requires energy, or work, which takes heat away from the parcel, so the air cools as it rises. This is called an adiabatic process. The term adiabatic means that no heat transfer occurs into, or out of, the parcel. Air has low thermal conductivity, so transfer of heat by conduction is negligibly small.
The rate at which the parcel cools as it is lifted is called the lapse rate. The lapse rate of a rising, unsaturated parcel (air with relative humidity less than 100 percent) is approximately 3 °C per 1,000 feet (9.8 °C per kilometer). This is called the dry adiabatic lapse rate. This means for each 1,000-foot increase in elevation, the parcel’s temperature decreases by 3 °C. Concurrently, the dewpoint decreases approximately 0.5 °C per 1,000 feet (1.8 °C per kilometer). The parcel’s temperature-dewpoint spread decreases, while its relative humidity increases.
This process is reversible if the parcel remains unsaturated and, thus, does not lose any water vapor. A descending (subsiding) air parcel compresses as it moves into an area of higher pressure. The atmosphere surrounding the parcel does work on the parcel, and energy is added to the compressed parcel, which warms it. Thus, the temperature of a descending air parcel increases approximately 3 °C per 1,000 feet (9.8 °C per kilometer). Concurrently, the dewpoint increases approximately 0.5 °C per 1,000 feet (1.8 °C per kilometer). The parcel’s temperature-dewpoint spread increases, while its relative humidity decreases.
The parcel and the surrounding environmental air temperatures are then compared. If the lifted parcel is colder than the surrounding air, it will be denser (heavier) and sink back to its original level. In this case, the parcel is stable because it resists upward displacement. If the lifted parcel is the same temperature as the surrounding air, it will be the same density and remain at the same level. In this case, the parcel is neutrally stable. If the lifted parcel is warmer and, therefore, less dense (lighter) than the surrounding air, it will continue to rise on its own until it reaches the same temperature as its environment. This final case is an example of an unstable parcel. Greater temperature differences result in greater rates of vertical motion.