Working & Features of Oil Temp Probe in Aircraft

Oil Temp ProbeFor the uninitiated, an oil temperature probe is required keep a check on the oil temperature. The oil temperature is vital to maintain its viscosity. A low temperature will make the oil useless whereas a higher than normal temperature will risk a whole lot more than just engine damage.

An oil temperature sensor is inserted into the aircraft engine (please see latter part of this article on how to install the oil temperature probe), and the wires are connected to the oil temperature indicator or EDM if your aircraft cockpit sports an EDM. If the EDM permits it, the pilot can pre-set an alarm for the oil temperature so an audio-visual alarm sounds if the temperature drops to below a certain level or raises above a certain level (usually 180F or thereabouts).

Since oil plays a vital role in any aircraft, the pilots need to ensure the oil temperature probe and gauge are not only in good working condition, they are also accurate. This is done by an expert mechanic who will spot oil temp probe / gauge calibration errors. All such errors need instant attention – either recalibration or a replacement.

Once the mechanic completes his task, it is best if the gauge, sensor, and interconnect wiring be calibrated by a qualified technician or agency before flight. This is deemed prudent as even a small 5% or 10% make a huge difference to the engine. The error could result in the pilot take unnecessary measures or not taking any measures. The latter especially could prove fatal. From experience, we can state that even new oil temperature probes need calibration – or at least testing to ensure the reading they provide is accurate.

These days however, with the arrival of IC based integrated avionics and LCD displays, engine data is generally more reliable than what they once were just a few years back.

J.P.I. manufactured EDM’s allow for the display of several different engine gauges on a small but clear to read LCD screen.

Installation of the oil temperature probe in aircraft

The Oil Temp Probes in aircraft is installed by removing the pipe plug located on the front of the engine inline with the push rods. This oil galley feeds the valve lifters. Insert the probe supplied with the kit and check for leaks after installation. The probe leads are routed back to the cockpit along with the EGT wires. Attach these to the appropriate gauge or EDM.

More information on oil temperature probes can be found here:


Aircraft Engine Monitoring Systems – How it Works

Aircraft Engine Monitoring SystemsCalled by various names including EDM (Engine Data Monitor), ECM (Engine Condition Monitoring) etc. these are essentially aircraft engine monitoring systems. These electronic monitoring cum display units are at heart, a very simple device and this article aims to explain in simple language, how these devices work.

There are two parts to any aircraft engine monitoring system:

1. The EDM / ECM itself and,
2. The probes

The probes:

If you have ever been inside the ICU of any hospital, you might have notice patients hocked up to a monitoring system. On the patient are attached various sensors all leading to the monitoring unit.

The sensor probes in any aircraft work in exactly the same way. These probes have a sensor housed within an appropriate metallic body that enables the mechanic to clamp it onto the aircraft engine. The sensor itself is usually inserted into the engine. The reading is transferred via electrical wires back to the cockpit and is then connected to the aircraft engine monitoring system.

Any aircraft – even the single engine ones have numerous probes. In days gone by, each probe used to be connected to its specific dial in the cockpit. The cockpit therefore used to have numerous dials and indicators. These days however, the probe converts the reading into an electrical pulse which is transmitted via electrical wires to the aircraft engine monitoring system.

The aircraft engine monitoring system:

In absolute simple terms, the aircraft engine monitoring system has three parts to it – display, intelligent data comparison and, data storage.

Display: Every EDM or ECM aims to display the data in a way that helps the pilot(s) to get the gist of what is happening inside the engines in a single glance! The data is presented graphically and in figures. Most EDM’s of today also permit the pilot to choose what is displayed and how.

Standard data comparison: Most EDM / ECMs permit the pilot(s) to key in upper and lower limits for every probe. The aircraft engine monitoring system compares the incoming values to the pre-entered upper and lower limits. So, if the EGT (Exhaust Gas Temperature) is approaching or is higher than the upper limit (or lesser than the lower limit), that was keyed in, the aircraft engine monitoring system will trigger an audio-visual signal thereby gaining the pilots attention.

Intelligent data comparison and analysis: Aircraft Engine Monitoring Systems can not only accept data from the probes inserted into various parts of the engine, it can also accept inputs from the GPS navigation and compare the navigation output with level of fuel in the tank. It can analyse and deduce whether there is enough fuel to complete the trip and provide this information to the pilots. If the pilot(s) change the destination the Aircraft engine monitoring system will recompute fuel availability in seconds.

Data storage: Aircraft engine monitoring system have built-in memory modules to store data. This stored data can be downloaded for analysis via the USB or other ports located on the aircraft engine monitoring system itself.

Engine Data Monitor 730 System Vs 760 System

Engine Data Monitor 730 System and 760 SystemWe present a comparison between EDM 730 and EDM 760 – both Engine Data Monitors are manufactured by JP Instruments; World leader in onboard flight instruments and aircraft engine data management systems.

JP Instrument’s aircraft engine data monitors provide the pilots with real time information for aircraft. These systems constantly monitor the health of the aircraft engine and any anomalies are instantly brought to the pilot’s attention via audio-video alarms. This leaves the pilots to concentrate on the flight experience rather than constantly monitoring the engines.

This article provides you with relevant information to compare two great engine data monitoring systems manufactured by J.P. Instruments; the EDM 730 and EDM 760.

EDM 730
From $1,557.00 to $3,965.00)

1. Easy to install.
2. Clear, Full-Colour Graphics
3. Easy-to-read data display
4. Easy to programme
5. Annunciation of exceedances.
6. More data per page – less page swapping.
7. Fully approved.

Package Form Factor:

1. Requires only 3-1/8″ space
2. Easy to adjust location.
3. 4 mounting options.
4. Just 65mm depth
5. Easily upgradable from 700 series JPI EDM’s.
6. Data download via USB port.
7. Pilot programmable parameters.
8. Horsepower display in percentage.
9. Just press button for Rich of peak or lean of peak operation.
10. Graphically display of RPM and manifold pressure.
11. Computerized fuel-flow system.
12. Fuel management can be linked to GPS.
13. EDM scanner function.
14. Display in portrait or landscape.
15. Ideal for 4/6/7/8/9-cylinder engines,
16. Turbocharged engines

1. JPI Carb Temp Option 10-27103
2. JPI RPM Option 10-01720
3. JPI Oil Temp Option 10-27100
4. JPI Oil Pressure Option 10-04075
5. JPI OAT Option 10-27095
6. JPI Manifold Pressure 10-04512
7. JPI TIT Option 10-27090

More information here:

EDM 760
From $3,675.00 to $8,1000.00)

Using the latest microprocessor technology, the EDM will monitor up to twenty-four critical parameters in your engine, four times a second, with a linearized thermocouple accuracy of better than 0.1 percent or 2 F° which has been verified and tested by the FAA and thus TSO’d (Technical Standard Order). The EDM is constantly “red-line” checking all 29 critical parameters (not 16) that are automatically checked FOUR TIMES A SECOND, regardless of current display status.

1. Latest microprocessor technology
2. Monitors 24-critical aircraft engine parameters – 4 times every second.
3. Linearized thermocouple for better accuracy – verified and tested by the FAA.
4. Uses just two buttons for all programming functions of the EDM.
5. Computer Assisted Diagnostics for the entire engine.
6. 29 Alarms, including Shock Cooling, EGT Differential, Fuel flow and Alternator Voltage.
7. Excellent variable scaling of EGT Bar Graph.
8. Patented LeanFind Mode automatically identifies the first and last cylinder to peak and while patented PeakFind system has quick responding probes to automatically capture EGT or TIT peak value.
9. USB Data Port.
10. FAA approved Fuel-flow monitoring system.
11. Alphanumeric scanning display of 29 functions or channels

1. EGT Probe PN- M111
2. PC Interface Cable for EDM 700, EDM 800 and EDM 760
3. ALternate USB Download Box
4. CHT Bayonet Probe

More information here:

Features and Specifications of CDT Probe in Aircraft

CDT ProbeA CDT probe is used in aircraft as well as in ships. The ones used in ships are known as Conductivity, Temperature and Depth probe. It provides data on water salinity or lack thereof, it’s temperature and water depth at current location.

The CDT probe used in aircraft on the other hand, is used to measure compressor discharge temperature of the aircraft compressor and is therefore installed in the engine compartment just ahead of the inter-cooler. The CDT probe kit for the aircraft usually comes accompanied with a stainless-steel clamp to be fitted around the air-port leaving the inter-cooler.

The CDT probe kit as supplied by US-based J.P Instruments features a thermocouple type ‘K’ CDT Probe along with a stainless-steel clamp thimble and also includes one stainless steel exhaust seal washer and one stainless steel screw type clamp.

The purpose of wanting to know the discharge temperature of the aircraft compressor is to prevent the possibility of detonation brought about by excessive heat in the compressor of the aircraft.

What usually happens is that, the aircraft intercooler cools the air so much that the upper limit of temperature is usually never reached. Basically, pilots need to know the inlet temperature limits for the aircraft engine and the temperature of the air at this point. So long as the CDT indicates a temperature reading that is below what the maximum should be, the aircraft is fine. If CDT temperature reading is above the upper limit, the pilot has to take a call on whether the conditions justify the reading.

As we are aware, CDT can be critical under certain circumstances e.g. staging a dual annular combustor for a high bypass turbofan commercial jet engine where fuel-to-air ration can be critical.

Specifications and working of the CDT in aircraft: To obtain the correct compressor discharge temperature reading, the probe is mounted externally but directly in the flow path of the air discharged from the compressor. As the air flows, it touches at least one thermocouple and data is returned to the indicator (or EDM) in the cockpit.

Basically, a hole bored into the engine case and the CDT is fitted into that. The exhaust air gets channelled into this hole and into the housing containing the CDT probe which in turn measures the air temperature. The CDT probe returns n electrical signal to the connected display unit or EDM Monitors mounted in the cockpit. Modern EDM’s can compare the current temperature with the pre-set max temperature and in the event of an anomaly, sound the appropriate audio-visual alarm.

What matters is the response speed of the CDT. Any temperature spikes should be brought to the pilot’s attention immediately – and this is where the JPI CDT scores. JPI’s grounded CDT Probes are manufactured using a space-age material, Hastaloy-X, capable of withstanding harsh sulphur atmosphere of temperature exhaust gas. Also, it’s 1/16″ in diameter cable is less susceptible to temperature loss and therefore are more accurate than the fatter temperature probes manufactured by the rivals. You can select and buy CDT probes here:

What is Manifold Pressure Sensor in Aircraft?

Manifold Pressure SensorAlthough it’s technically termed as aircraft manifold pressure monitoring, the word “pressure” in this case, is a bit of a misnomer. This is because the aircraft manifold pressure data is not about pressure but suction.

The cylinders in any aircraft engine are like a large suction pump because the cylinders are constantly sucking air into itself. The MAP sensor therefore, if anything, is reading suction not ram air pressure. So at idle power your MAP gauge might display between 10 and 12 inches when actual pressure outside is 30 inches. This means your engines are actually starving for air creating a vacuum pressure within the intake manifold.

As the piston descends with the inlet valve open, a partial vacuum is created. It is this vacuum sucks in fuel into the intake. Therefore, greater the vacuum, greater the air-fuel mixture and hence greater the power output from the aircraft engine.

So, the more air-fuel mixture pumped into the cylinders, the more power the engine develops and enables us to fly higher or faster. Now, if we measure air pressure in the induction system, just before it enters the aircraft cylinders, we will have a good idea of how much power we can develop.

In any normally aspirated aircraft engine (non turbo-charged), the manifold pressure gauge usually has a range of 10 to 40 in. hg. In a turbocharged engine, the limits as per manufacturer settings. Effectively, when the engine is shut down, the MAP should read roughly the same as current atmospheric pressure setting.

Generally, MAP sensors are used in fuel injected aircraft engines. These days, the manifold absolute pressure sensor provides instant manifold pressure data (as described above) to the engine’s electronic control unit (ECU).

The data presented by the MAP is used to figure out the density of the air and calculate the engine’s air mass flow rate. These figures in turn help the pilot determine the required fuel mix for the most optimum (or economical) combustion. This helps work out the ignition timing.

Alternatively, fuel-injected engine can also use the mass airflow sensor (MAF sensor) to detect the intake airflow. In most naturally aspirated engines, there is either of the above two. In forced induction engine however, both tend to be deployed. Usually the MAF sensor is parked on the intake tract pre-turbo while the Manifold Pressure Sensor is installed on the charge pipe leading to the throttle body.

A lesser known fact is that the aircraft’s MAP sensor data can easily be converted to air mass data using the speed-density method. For this, the air temperature and engine speed in RPM Sensor are used.

Typically, modern EDM’s use MAP sensor data for on-board diagnostics (EBD), to test the functionality of the exhaust gas recirculation (EGR) valve.

What is a Fuel Flow Transducer in Aircraft?

Fuel Flow TransducerFuel flow transducers came to be used in aircraft around the early 70s. Vibration of an aircraft engine. It also had to meet the important FAA regulation regarding blocked rotor pressure drop which could not be more than 1.5 times the spinning rotor pressure drop. Fuel flows can be measured via a conventional rotor-based fuel measurement system or, via the more modern fuel flow transducer – a digital-technology based system. The advantage of this new technology fuel flow measurement system is that, it is impervious to pressures and therefore the data is more accurate.

The fuel flow transducer works upon a vane RPM sensor that is usually located behind the fuel filter and works in combination with the manifold air pressure (MAP). The fuel flow transducer produces a current-pulse signal from an opto-electronic pickup that’s fitted with a preamp. The signal amplification enables it to measure fuel flow that is as low as 0.3 gal/hour and this makes it more accurate than the conventional fuel flow measuring systems.

Here’s how the Fuel Flow Transducer works: The fuel enters the flow chamber within the fuel flow transducer and begins moving along a helical path. This is to vent out any vapour bubble that might be present in the fuel and result in wrong reading. The rotational velocity of the liquid is directly proportional to flow rate. A neutrally buoyant rotor spins with the liquid between V-jewel bearings. Rotor movement is sensed when notches in the rotor interrupt an infrared light beam between an LED and phototransistor. Generally, the fuel flow transducer operates on 12 to 15V consuming just 30 to 50 mA. The red wire is +V power, black is ground and the white wire is signal. Although it contains digital technology, the fuel flow transducer can operate at temperatures between -55°C to 70°C.

If you have a IO-540 300 HP engine with electric and engine driven pumps, the fuel flow transducer should be placed downstream of the engine pump and before the servo. Also, if you have a Rotax 100 ULS (dual carbs), the fuel flow transducer needs to be plumbed in just before the fuel pump – you do not need a second fuel flow transducer. When using a fuel scanner, please use only recommended fuel flow transducers – these are listed in the fuel scanner manual. For e.g. if your fuel scanner is manufactured by JPI use only JPI fuel flow transducers. Although fuel flow transducers work the same, there are minor internal variations and these will match the fuel scanners they are supposed to be paired with. So, using fuel flow transducer from a different manufacturer can result in erroneous Fuel Flow Instruments reading.

The best fuel flow transducers are manufactured by JP Instruments more information here:

What are the functions of Induction Air Temperature (IAT) probe?

Induction Air Temperature ProbeWe all know that every combustion engine (except maybe in rockets), rely on an external air source for combustion. Problem for aircraft is that, the air entering the combustion chamber may not always have the ideal temperature for a healthy combustion.

Cold air usually found at high altitudes for example, is denser than air at sea level. Cold air being denser, requires more fuel otherwise an air-fuel ratio imbalance occurs and the combustion will be erratic. If the combustion in an aircraft engine is erratic, and you know what will happen. So, when the air is colder than optimum temperature, there are two things you can do – either warm the air or squirt more fuel. Obviously, the latter is not an ideal solution because the aircraft can only carry as much fuel as the tanks will hold.

But before you can do anything, you need to know what the air temp is and that is where the induction air temperature or IAT probe in aircraft comes in. The function of the modern induction air temp therefore, is to sense and digitize the temperature of the air that is to flow into the combustion chamber.

Modern day aircraft have an onboard computer that automatically balances the air-to-fuel ratio. The IAT probe (apart from sending data to the EDM Monitors) provides air temp data to the onboard engine computer that controls the aircraft engine. The onboard computer in turn, dynamically alters the air-to-fuel ratio by changing the timing of the injector pulses.

The Intake Air Temperature (IAT) probe is mounted in the air intake manifold of the aircraft. The tip of the IAT probe is exposed to external air entering the aircraft engine. Essentially, the IAT probe is a thermistor, so its electrical resistance changes in response to changes in the temperature of the sensor. This means that the return voltage from the IAT probe changes in proportion to changes in air temperature.

If the aircraft is experiencing combustion related issues, chances are, the IAT probe might be malfunction and that can happen if it gets coated with oil, sooth, feathers, dust and so forth. Loose or corroded wiring or connectors can also have the same effect. If the IAT probe transmits inaccurate voltage, the onboard engine computer will miscalculate the air-to-fuel mixture and this could result in a rich or lean fuel mixture.

The resistance and voltage test specifications for your aircraft’s IAT probe can be found in your aircraft service manual and the leaflet that came with the IAT probe (if you’ve purchased a new one).

Once every few weeks, it would be a good practice to test your aircraft’s IAT probe and also check area around the probe to ensure it is free of oil and anything else that might contribute to inaccurate temp feedback.