An instructor reported departing with a student for training in a tecnam eaglet when the battery mas...

Narrative:

During a training flight in the tecnam eaglet the student and I preflighted the aircraft and was able to turn on the master switch to extend the flaps. Later we tried to turn on the master switch to start the aircraft and it would not turn on to start the aircraft. I figured the battery must have died and tried to call the maintenance department. They had left for the day so we continue trying to trouble shoot the problem. Eventually; after about ten minutes; the master switch turned on after many attempts at turning the switch on and off.we decided to go fly since we now could start the aircraft. The run-up and taxi went fine. We took off on runway 35. During takeoff I noticed the student needed help with what appeared to be a crosswind. To assist I used some input on the ailerons and then let the student have back full control after takeoff. As we were climbing out I noticed an acrid burning smell that smelled like burnt plastic. I asked my student if he smelled anything and at first he said that he didn't; but then he said he did.I ask tower if we could come back around and land. He said we could and asked what the situation was. I explained that I was smelling something burnt and that I wanted to land because of that. He approved us to make right traffic back to 35. As we were turning around I decided that I should get the aircraft on the ground as soon as possible so I asked if I could land on 17. The controller asked if I was [in need of priority handling] and I confirmed that I was. We were cleared to land on 17 and during landing I felt like I had a crosswind again even though I believe the winds were under 5 knots. During the landing I realized I had a flat tire on the left main. I brought the aircraft to a stop and air traffic control asked if I needed any further assistance. I said that I had a flat tire and would need assistance. The fire trucks came out to look for hot spots; but found none. I was towed off of the runway and returned to the flying club.the aircraft was later inspected and blackened wires were found behind the master switch which explains the problems and the smell. The tire may have flattened during takeoff which may be why I felt a crosswind right before liftoff. The tire may have flattened because of the student holding the brakes; which if he was; I didn't notice. The tire may have been worn already to the point it was ready to give out. I couldn't fully inspect the tire before takeoff because of fairings on the wheels. It's possible the tire went flat during the landing although the landing was smooth and braking was not excessive. I don't think it's possible to know when the tire went flat. I have not heard back from the maintenance department the cause of the flat tire.hopefully this information can be used to improve safety.

Original NASA ASRS Text

Title: An instructor reported departing with a student for training in a Tecnam Eaglet when the battery master switch malfunction and almost immediately detected a burning electrical odor so they returned to land. On landing; they discovered a main tire flat; but were uncertain when it deflated.

Narrative: During a training flight in the Tecnam Eaglet the student and I preflighted the aircraft and was able to turn on the master switch to extend the flaps. Later we tried to turn on the master switch to start the aircraft and it would not turn on to start the aircraft. I figured the battery must have died and tried to call the maintenance department. They had left for the day so we continue trying to trouble shoot the problem. Eventually; after about ten minutes; the master switch turned on after many attempts at turning the switch on and off.We decided to go fly since we now could start the aircraft. The run-up and taxi went fine. We took off on Runway 35. During takeoff I noticed the student needed help with what appeared to be a crosswind. To assist I used some input on the ailerons and then let the student have back full control after takeoff. As we were climbing out I noticed an acrid burning smell that smelled like burnt plastic. I asked my student if he smelled anything and at first he said that he didn't; but then he said he did.I ask Tower if we could come back around and land. He said we could and asked what the situation was. I explained that I was smelling something burnt and that I wanted to land because of that. He approved us to make right traffic back to 35. As we were turning around I decided that I should get the aircraft on the ground as soon as possible so I asked if I could land on 17. The controller asked if I was [in need of priority handling] and I confirmed that I was. We were cleared to land on 17 and during landing I felt like I had a crosswind again even though I believe the winds were under 5 knots. During the landing I realized I had a flat tire on the left main. I brought the aircraft to a stop and air traffic control asked if I needed any further assistance. I said that I had a flat tire and would need assistance. The fire trucks came out to look for hot spots; but found none. I was towed off of the runway and returned to the flying club.The aircraft was later inspected and blackened wires were found behind the Master Switch which explains the problems and the smell. The tire may have flattened during takeoff which may be why I felt a crosswind right before liftoff. The tire may have flattened because of the student holding the brakes; which if he was; I didn't notice. The tire may have been worn already to the point it was ready to give out. I couldn't fully inspect the tire before takeoff because of fairings on the wheels. It's possible the tire went flat during the landing although the landing was smooth and braking was not excessive. I don't think it's possible to know when the tire went flat. I have not heard back from the maintenance department the cause of the flat tire.Hopefully this information can be used to improve safety.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1399658
Time
Date	201610
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Light Sport Aircraft
Operating Under FAR Part	Part 91
Flight Phase	Initial Climb
Flight Plan	None
Component
Aircraft Component	Electrical Wiring & Connectors
Person 1
Function	Instructor Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Instrument
Experience	Flight Crew Last 90 Days 200 Flight Crew Total 900
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor

An instructor reported departing with a student for training in a tecnam eaglet when the battery master switch malfunction and almost immediately detected a burning electrical odor so they returned to land. On landing; they discovered a main tire flat; but were uncertain when it deflated.