Aircraft Accidents - Page 4 Aviation Articles

Aircraft Spins 101


Photo: H. Rabb/Wikimedia
As mentioned in my previous article on stalls, accidents that occur due to stall/spin scenarios are more fatal than others. According to an AOPA study, stall/spin accidents have a fatality rate of about 28 percent, higher than the overall average fatality rate of 20 percent.

A spin occurs when an airplane stalls in an uncoordinated or aggravated state. If a recovery is not initiated after an uncoordinated stall occurs, the wing that is more stalled than the other will drop and the nose will follow into a spiraling descent. The aircraft will descend rapidly in a corkscrew motion.

According to the Jeppesen Private Pilot Manual, a small airplane will descend about 500 feet for each turn in a spin, so there's not much altitude or time available for a recovery in many cases. Considering stalls and spins often occur at low altitudes to begin with, it's clear why the fatality rate is higher for these accidents.

Stages of a Spin
The FAA has outlined three stages for spins in light aircraft: incipient, fully developed and recovery.

  • Incipient: The incipient phase of a spin is the stall and spin entry, up to about 2 turns in the spin.
  • Fully Developed: When the airspeed and rotation stabilize, the spin is considered fully developed.
  • Recovery: Recovery occurs when the pilot applies rudder and aileron inputs to counter the spin and the aircraft regains lift and control function. Once the inputs are initiated to stop the spin, the aircraft can usually recover in less than one spin.

Types of Spin

  • Erect Spin: Erect spins are the most common type of spin, occurring when the aircraft rolls and yaws in the same direction and the aircraft is upright and in a slightly nose-down attitude.
  • Inverted Spin: An inverted spin occurs when the aircraft spins upside down and yaw and roll occurs in opposite directions.
  • Flat Spin: Getting its name from the flat-like pitch attitude, the flat spin occurs when the aircraft spins at a level pitch attitude around the vertical axis as a result of a yawing motion alone. Flat spins are the most difficult to recover from (and just as difficult to enter in some aircraft!)

 

Spin Recovery
Spin recovery should be initiated at the first sign of a spin. Recovery procedures are specific to the aircraft flown and are found in the pilot operating handbook of each aircraft. In light aircraft, the spin recovery procedures follow a typical pattern and can be remembered by the common acronym PARE.

P - Power: The throttle should be moved to the idle position to reduce thrust.
A - Ailerons: Ailerons should be neutralized.
R - Rudder : Full opposite rudder input should be applied until the rotation is stopped. If the aircraft is rotating to the left, right rudder should be applied. Once the spinning stops, the rudder should be neutralized.
E - Elevator: Quick forward pressure should be applied to break the stall and gain airflow over the wings. Once the aircraft gains lift, back pressure should be applied gradually so as not to stall again.

Training aircraft are stable by design. They're meant to recover from unusual attitudes without much external control input from the pilot. A Cessna 172, for example, is actually somewhat difficult to perform an intentional spin in. But this doesn't mean that pilots of training aircraft are immune to spins.

While intentional spins are not always demonstrated during training, stall and spin awareness should always be emphasized with flight students. Many pilots tend to become confident in stall recovery, but all pilots would be wise to remain familiar with spin entry characteristics and recovery procedures for their specific aircraft.

How Well Do You Know Your Stalls & Spins?


Image: Theresa Knott/Wikimedia Commons

For new flight students and passengers, an aircraft stall can often be a source of fear. What is a stall? Will the airplane fall out of the sky? Does the engine quit?

And while stalls shouldn't be something that pilots fear, they should be taken seriously. Aircraft stalls and spins remain a leading cause of general aviation accidents - causing ten percent of general aviation accidents, according to one AOPA study. And stall/spin accidents result in more fatalities than other types of aircraft accidents. Private and commercial pilots are most likely to enter a stall, while student pilots and ATPs are less likely to stall, according to AOPA.

A 2012 advisory circular claims that loss of control accidents are a growing problem and that inappropriate reactions to stall indications are part of that problem.

What's a Stall?
Let's start with the basics. For those of you non-pilots, you need to know that an aircraft stall has absolutely nothing to do with the engine (unless we're talking about compressor stalls - an entirely different topic). Instead, an aircraft stalls when the airflow over the wing is disrupted enough to cause a loss of lift.

Stalls are dangerous because control surfaces become inadequate to control the flight, and if a recovery is not initiated, the aircraft will quickly lose altitude. And then there's that deadly spin: If uncoordinated, a stall can develop into a spin.

The FAA defines an aircraft stall as "an aerodynamic loss of lift caused by exceeding the airplane’s critical angle of attack."

The critical angle of attack is the key phrase here. The angle of attack is the angle between the chord line of the wing (an imaginary line running from the leading edge of the wing to the trailing edge) and the relative wind. The critical angle of attack is the angle at which maximum lift is produced. An increase in the angle of attack beyond the max coefficient of lift results in a loss of lift, airflow separation over the wing and a subsequent stall.

An aircraft can stall at various airspeeds, altitudes, pitch attitudes, configurations and weights. But the critical angle of attack must be exceeded for a stall to occur.

Types of Stalls

  • Power on stall: A power-on stall occurs during situations in which the aircraft power or thrust is increased quickly, such as during takeoff. Power on stalls usually occur (not always) with gear and flaps up.

  • Power off stall: Power off stalls occur when the aircraft power is decreased or at idle, such as during landing. Power-off stalls tend to occur with gear and flaps down.

  • Elevator trim stall: If the pilot disregards the elevator trim setting, any abrupt change in power or configuration can initiate a stall. This can happen easily during takeoff or go-arounds, when the aircraft trim tab is adjusted for the descent and a go-around is initiated. The aircraft can pitch up quickly and unexpectedly to a high angle of attack.

  • Cross controlled stall: A cross-controlled stall is one of the most dangerous types, as it's an uncoordinated stall and easily transitions to a spin. A cross-controlled stall occurs when the pilot inputs aileron control in one direction and rudder pressure in the opposite direction. Cross controlled stalls are known to occur during turns in the traffic pattern.

  • Accelerated stall: When excessive loads are placed on the airplane (such as during steep turns), an aircraft is capable of stalling at a higher airspeed and/or a lower pitch attitude than the pilot might be accustomed to.

  • Secondary stall: Secondary stalls occur if a pilot attempts to recover from a stall too quickly by pitching up to recover from the dive before obtaining an appropriate airspeed and generating enough lift.

  • Deep stall: Also called a super stall, the deep stall happens in T-tail aircraft, like this Piper Lance II or this King Air 350. It occurs when the airflow over the wing is disrupted and airflow over the tail of the aircraft is also disrupted, rendering both the ailerons and elevator/rudder ineffective at the same time. In a deep stall, recovery is difficult and sometimes, impossible.

Spins
An uncoordinated stall can result in a spin. According to the FAA Airplane Flying Handbook, a spin is an aggravated stall that results in autorotation - a downward corkscrew motion.

The spin is a result of one wing being at a higher angle of attack than the other, often descried as one wing being "more stalled than the other." The difference in angles of attack creates lift on the less stalled wing and drag on the more stalled wing.

Spins are more difficult to recover from, as altitude is lost very quickly and control surfaces may react different than the pilot expects, which is why it's important for pilots to continuously practice stall and spin recovery.

Mayday, Mayday, Mayday! - the Origin of a Distress Call

In honor of May Day (May 1st, a holiday associated with the beginning of spring and the labor movement in many counties), I thought I’d take a moment to explore how the same word came to mean HELP in aviation!

The term Mayday is used internationally as a distress signal in voice procedure radio communications. It derives from the French venez m'aider, meaning "come help me". It is used to signal a life-threatening emergency by many groups, such as police forces, pilots, firefighters, and transportation organizations. The call is always given three times in a row ("Mayday Mayday Mayday") to prevent mistaking it for some similar-sounding phrase under noisy conditions, and to distinguish an actual Mayday call from a message about a Mayday call.

The Mayday procedure word originated in 1923 by Frederick Stanley Mockford (1897–1962). A senior radio officer at Croydon Airport in London, Mockford was asked to think of a word that would indicate distress and would easily be understood by all pilots and ground staff in an emergency. Since much of the traffic at the time was between Croydon and Le Bourget Airport in Paris, he proposed the word "Mayday" from the French m’aider.

Before the voice call "Mayday", SOS was the Morse code equivalent of the Mayday call. In 1927, the International Radiotelegraph Convention of Washington adopted the voice call Mayday in place of the SOS Morse Code call.

Other emergency calls include "Pan-Pan" (from the French: panne – a breakdown), or simply "declaring an emergency" – although the International Civil Aviation Organization (ICAO) recommends using the two terms above to prevent confusion and errors in aircraft handling. The use of these terms without proper cause could render the user liable to civil and/or criminal charges.

Now to come full circle, I leave you with a related scene from one of your favorite aviation films.

Live-Streaming: The Future of Flight Tracking?

The disappearance of Malaysia Airlines Flight 370 once again raises questions about the real-time tracking of aircraft. MH370 remains missing after controllers lost contact with it on March 8th. Authorities have assumed the Boeing 777 crashed in a remote area of the Indian Ocean.

The idea of real-time flight tracking has been discussed before, namely after Air France Flight 447 went missing and was later found in the ocean in 2007. It took investigators almost two years to recover the flight data recorder after the A330 crashed into the Atlantic Ocean while en route from Rio de Janeiro to Paris. Afterward, the public and industry folks alike wondered how we can manage to locate missing cell phones, but not missing aircraft? Even with the addition of NextGen technology like data link and ADS-B that's on board aircraft today, it's strangely not enough to find a missing airliner.

While the search for MH370 continues, industry groups are once again revisiting the idea of a live-streaming flight recorder for airliners. While the costs associated with it aren't anything that airlines want to pay, many believe that the cost is minimal when compared to the added benefits, and that it's an obvious remedy for cases like MH370 and AF447.

The NTSB is one industry group that is still interested in the concept of live-streamed data from aircraft. According to Reuters, the NTSB plans to continue to examine potential solutions that could include real time streaming of aircraft data from the flight recorder or ACARS, or both.

What About ACARS?
Currently, many planes are equipped with data tracking services like ACARS - data link technology that uses VHF and satellite communication to gather data from sensors on the aircraft. The data is sent from air to ground at certain times during the flight, transmitting things like flight times, location and fuel usage to air traffic controllers and dispatchers. The ACARS system on MH370 was disabled in flight, but satellites were still able to "ping" the aircraft about once per hour.

Why Can't We Stream Flight Recorder Data?
The short answer is that we can. The technology is there, according to this New York Times article. The cost, however, is prohibitive. And the logistical demands associated with thousands of airliners transmitting real-time data all day aren't there yet. And according to the New York Times article, the infrastructure required for constant live-streaming from thousands of airliners would be huge.

To become equipped for live-streaming, airlines would pay $50,000- 100,000 per airplane, according to some sources, and an additional cost for the service might range from $5-10 per minute. In an already cash-strapped industry, airlines just aren't going to pay that much if they don't have to.

Future Technology
The conversation doesn't end there, though. At least one supplier, Flyht Aerospace Solutions, Ltd., is already able to stream black box data in an emergency.

Flyht claims that while live-streaming technology on airline flights is an investment, there is also a cost-benefit involved. Security isn't the only topic at hand here: Live-streaming of data can alert airlines of maintenance issues immediately, instead of hearing about it after the flight lands or minutes or hours after the event. It also allows for better monitoring of new procedures and the system can record data for future safety and cost analysis. Operators would be able to implement improvements and safety measures with this kind of access to data.

And of course, in the wake of MH370, a more secure system of tracking airliners would be a welcome one. Live-streaming of aircraft data could ensure that an aircraft never disappears again (as long as the system can't be easily disabled or manipulated from the cockpit.)

What's your opinion? Should future airline flight data be live-streamed?

The Importance of WAAS with LPV

Mark Wilken – Director of Avionics Sales with Elliott Aviation
www.elliottaviation.com

Traditionally, ground-based landing systems have been the only method for low visibility approaches. Many business aircraft, however, are operated from airports without ground-based systems and are restricted to using non-precision approaches. If your aircraft is equipped with WAAS and LPV you have many more options to get to where you are going safely and efficiently.

There is a common misconception in the industry that WAAS and LPV are one in the same, however, they are two completely different systems.

WAAS, or Wide Area Augmentation System, was developed by the FAA to augment GPS to improve accuracy. Put simply, it is a corrected GPS. It is accurate to about one meter of your actual position. Combined with LPV, it can get you into more airports in a more direct manner. Without LPV, WAAS is just nothing more than an accurate sensor.

LPV, or Localizer Performance with Vertical Guidance, gives you an enhanced database in your FMS GPS and allows ILS-like approaches at airports that do not have an ILS or ground-based system. LPV approaches allow for minimums to be as low as 200 feet.

If LPV approaches are not available at the airport you are traveling, they likely have LP approaches available. LP, or Localizer Performance Approaches, provide precision lateral guidance using the enhanced accuracy WAAS provides. As an example, an LP approach into Telluride, Colorado allow for minims of an additional 460 feet for days when the weather is less than perfect.

Mark Wilken is the Director of Avionics Sales for Elliott Aviation which employs over 40 avionics technicians at their headquarters in Moline, IL. Mark began his career at Elliott Aviation in 1989 as a bench technician repairing radios and quickly became the manager of the department. Mark helped launch Elliott Aviation’s Garmin G1000 retrofit program where the company has installed more King Air G1000’s than all other dealers in the world combined. Recently, he has headed STC programs for the newly-launched Aircell ATG 2000 system for Hawker 8000/850/900, Phenom 300 and King Air 350/B200/B200GT. Mark is a licensed pilot and holds an associate’s degree in avionics and a bachelor’s degree in aviation management from Southern Illinois University.

Elliott Aviation is a second-generation, family-owned business aviation company offering a complete menu of high quality products and services including aircraft sales, avionics service & installations, aircraft maintenance, accessory repair & overhaul, paint and interior, charter and aircraft management. Serving the business aviation industry nationally and internationally, they have facilities in Moline, IL, Des Moines, IA, and Minneapolis, MN. The company is a member of the Pinnacle Air Network, National Business Aviation Association (NBAA), National Air Transportation Association (NATA), and National Aircraft Resale Association (NARA).

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