Transponder Aircraft

Transponder Aircraft - GPS satellites transmit less than five watts of power, so by the time the signal reaches you, it is very, very weak. Because of this, the GPS antenna has a built-in amplifier to boost the signal for the receiver.

Additionally, the GPS frequency is so high (in the gigahertz band) that the signals travel in a line-of-sight manner. This makes receiving the signal susceptible to airframe shadowing, thus mandating that a GPS antenna be mounted at the very top of the fuselage.

Transponder Aircraft

Altimeter (FAR 91.411): The aircraft's static system, altimeter, and automatic altitude-reporting (Mode C) system must have been inspected and tested in the preceding 24 calendar months before flying IFR in controlled airspace. FAR 43 Appendix E, Altimeter System Test and Inspection, lists the items that must be checked.

Gps Antennas

This technology allows ground controllers to track aircraft as they taxi. This has been a great step forward in improving safety as some of the world's largest airports can be a maze to navigate around and when fog reduces pilot visibility to near zero!

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Before the pilot begins to move from their hanger they too must obtain permission from air traffic control. During this initial contact, the air traffic controller MAY issue the pilot to input a certain squawk code or the pilot will fly under the generic code of 1200.

Transponders are an expensive item and for owners who like to fly around the wilderness and stay away from populated areas then the need to have one fitted is not worth the cost. For aircraft regularly operating in and out of airports there are a few rules:

For Helicopters And Small Aircraft

In my case, our Bonanza is equipped with an Aspen EFD1000 Pro primary flight display, a backup mechanical altimeter, L3 Lynx ADS-B transponder, and Trans-Cal solid-state encoder. The Aspen, Lynx, and Trans-Cal passed with flying colors, but the altimeter required adjustment to get within the required 25-foot accuracy.

Two years ago, the same inspection found a large leak in the static system from a failed fitting. And so, even though I grumble every two years about having to bring the airplane to the avionics shop for its biennial checkup, it seems that the process remains money well spent.

Until next time, I hope you and your families remain safe and healthy and wish you blue skies. The capability to perform timely onboard software loads provides operators with simplified upgrades, increased aircraft utilization and lower maintenance costs.

In addition, the high reliability of the NXT-series greatly enhances the overall validity of the TCAS system reducing Mode S transponder-induced No-Fault-Found (NFF) TCAS failures. L3Harris' Mode S Transponders meet the future needs for optimized flight and Air Traffic Modernization efforts for helicopters, business jets and regional aircraft by providing NextGen Automatic Dependent Surveillance – Broadcast (ADS-B) capabilities they need to operate safely and efficiently.

Software Upgradability Yields Reduced Maintenance Costs

The NXT family reduces lifetime costs and enables pilots to take advantage of more efficient routing which results in increasing airspace capacity, situational awareness and overall operational safety. Additionally, the high-reliability of the units enhances the overall surveillance system by reducing TCAS no-fault-found failures.

One which just shows the traffic advisory (TA), it displays the other aircraft's data, shows the position of other aircraft, and leaves it to the pilot to decide what action to take to maintain separation. Primary Radars transmit radio waves that bounce back after hitting an object, the time taken for the wave to return is used to calculate the distance of the object from the radar.

The radar antenna constantly rotates through 360° and the direction the radar antenna is pointing when the signal is received back is the location the aircraft is in from the radar. This is what places 'The Diamond' icon on the radar controller screen.

Hopefully, you'll never have to use an emergency locator transmitter antenna, but in case you do, they are designed to survive an "unscheduled" landing. They are almost always on the upper skin of the empennage and are made of a flexible material.

Emergency Locator Transmitter Antennas

There are a few exceptions, though; some may be buried in the vertical tail or look like small com antennas. A transponder works by passing digital information to any radar signal that it receives. The transponder takes flight data from the aircraft sensors and sends it with each interrogation from a radar, whether that be a ground-based or aircraft-based radar.

Transponders only pass data outward. The need for these inspections seems obvious. After all, if you're flying in controlled airspace, the air traffic controller is using your transponder's signal, including the altitude from the encoder, to provide traffic separation between you and the other aircraft.

And, if you're flying IFR, it's critical that you're actually at the altitude that your instruments indicate. However, avionics and instrument technology has evolved dramatically from the time that these regulations were originally written. I thought this might be a great opportunity to answer the question, while I'm waiting at Infinity Aviation in Nashua, New Hampshire, for my own aircraft's FAA-mandated biennial inspection of the pitot/static system, altimeter, and transponder.

Whenever any of the codes marked in red are typed into the transponder by the pilot it brings up an instant alert on the air traffic controller's radar screen to alert them that the aircraft needs assistance.

How Does A Transponder Work?

Syed has a Bachelor's Degree in Computer Science before he enrolled in flight school in 2016 where he was awarded his Fixed-Wing CPL with Frozen ATPL. He flies as often as he writes and passing on his love for aviation is one of his greatest passions.

L3Harris' NXT-600 / -700 / -800™ Mode S Transponders are ready to provide civil, commercial and military aircraft and helicopter manufacturers and owners with all the capabilities they need to operate safely and efficiently by providing the precise ADS-B Out (

DO-260B) flight data information. Normally, transponders are switched on before entering the active runway and switched to standby mode once vacating the runway after landing. However, with the passage of time, airports have started utilizing technologies such as surface movement radar and guidance which requires that the transponder be switched on once the pushback begins.

High-level of ADS-B Out (DO-260B) reporting requires the transmission of precise, real-time flight data information, including current aircraft position, speed and intent. The NXT-600 automatically transmits all position data via ADS-B Out to other nearby aircraft (equipped) and Air Traffic Control (ATC).

Highly Accurate Position Reporting

Squawk codes that are assigned by an air traffic controller are unique 4-digit codes that are assigned to each individual aircraft. Two aircraft cannot have the same squawk code within the same airspace. These squawk codes are usually assigned with the initial clearance either before taking off or entering the airspace.

Squawk codes are 4-digit codes assigned to a pilot from an air traffic controller. They allow the controller to see the aircraft on their radar screen along with information about their position. Each aircraft gets assigned a unique squawk code to allow easy identification on a busy radar screen.

Traditional analog altimeters are mechanical instruments that use a sealed bellows to move a dial to indicate your altitude. Over the years, moisture, temperature, dust, corrosion, and many other factors affect the accuracy of the instrument.

And so, altimeters routinely require testing and adjustment to ensure that the altitude displayed is within 25 feet of the altitude indicated by calibrated test equipment. Similarly, older encoders also use a combination of mechanical and electrical designs to send the aircraft's altitude to the transponder (with similar failure modes and adjustment requirements).

Controller-Assigned Codes

The transponders from the days of yore used analog “cavity tubes” that were prone to failure and calibration issues. All of this added up to a high likelihood that the biennial check of all these instruments would find enough issues to make the inspection requirement for the entire general aviation fleet well warranted.

Hi, I'm Rick James and I'm an aviation nut! I'm an ATP rated helicopter pilot & former flight instructor with over 3500 hours spanning 3 countries and many different flying jobs. This website was created to help pass on information and knowledge of all things aviation!

Communications radios can cause a lot of interference with GPS, because of the proximity of the panel units or their antennas. Therefore, it is important that the com and GPS antennas be mounted as far apart as possible.

Sometimes a com antenna must be relocated to the bottom of the aircraft. Each aircraft within that air traffic controllers sector is assigned a unique squawk code so that each aircraft can be identified easily upon departure.

What Are Squawk Codes?

During flight as the aircraft passes into a different airspace sector, the new air traffic controller looking after that sector may assign the aircraft a new squawk code to which the pilot must enter. TCAS acts like a mini radar and sends out interrogation signals from the aircraft.

When another aircraft is in the area its transponder responds to this interrogation and sends its data to the requesting aircraft. The TCAS system then decodes this information and places it on a screen in the cockpit for the pilots to see:

Prior to pushback, when the aircraft is at the gate, the pilots request a clearance known as an IFR clearance. As part of this clearance instruction, the air traffic controller will assign the pilot a 4-digit code known as the Squawk Code.

The pilot will type this code into their transponder ready for departure (PRESET BOX): Secondary Surveillance Radar (SSR) uses electronic pulses to interrogate the target aircraft. It is the SSR that gathers the flight data from the aircraft to display with the aircraft target on the air traffic controllers' screen.

For Commercial Airliners

Marker beacon signals are highly directional, which means you have to be almost directly over the transmitting ground station to receive them; therefore, marker beacon antennas need to be on the bottom of the aircraft. There are a few different types of marker antennas;

the more common types look like little canoes about 10 inches long. For some installations, Cessna has used flush antennas that appear to be flat plates under the empennage. It also has used an antenna that consists of a thick wire that protrudes straight down out of the empennage and then makes a turn toward the tail.

Transponders (FAR 91.413): The transponder must be inspected every 24 calendar months. FAR 43 Appendix F, ATC Transponder Tests and Inspections, lists the items that must be checked. To use a transponder, it must be inspected every 24 calendar months.

Additionally, the installation of or modification to a transponder must be inspected for data errors as well. A newer version is the one that detects the traffic and gives traffic advisory (TA) and when crucial, also provides resolution advisory (RA).

Marker Beacon Antennas

By resolution advisory, I mean that it verbally announces to the pilot to go left/right/climb/descend and these advisories have priority over air traffic controller's command. This resulted in a collision with a Boeing 737. The Embraer private jet managed to land at a military field where the occupants were detained, unfortunately, the Boeing 737 crashed in the Amazon jungle with none of the passengers or crew surviving the crash.

The VHF nav antenna is almost always mounted on the vertical tail, and there are three types: the cat whisker, the dual blade, and the towel bar. The cat whisker consists of a couple of rods jutting out from each side of the vertical stabilizer at a 45-degree angle.

But the cat whisker antenna is poor at receiving signals from the side. The dual blade is just that, two blades, one on each side of the tail. The towel bar resembles the common bathroom fixture, one on each side of the tail.

The blade and towel bar antennas have equal receiving sensitivity from all directions. A single nav antenna almost always feeds multiple nav receivers and sometimes the glideslope as well. Therefore, a failure in the nav antenna system would cause multiple systems to malfunction.

Nav Antennas

But, what about now? With solid-state transponders and encoders being the norm, and a growing fleet of glass panels with no mechanical altimeters or airspeed indicators, do these routine inspections still make sense? I had that very discussion with Jeff Wall at Infinity Aviation and was surprised to hear that the answer was an emphatic “Yes.”

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