A system for detecting radon activity and volcanic ash in an airspace in which an aircraft is flying, the system comprising: a detection system being configured for measuring radon activity and volcanic ash in the airspace in which the aircraft is flying, the detection system comprising: a probe configured for collecting air samples along a flight track of the aircraft in at least one chamber configured for measuring radon activity and volcanic ash in the air samples collected and configured for outputting a radon activity signal indicative of measured radon activity and a volcanic ash signal; and a processing unit configured to determine if the measured radon activity is above a predetermined critical value (A crit) representative for the flight altitude in which the air sample is collected within the probe, the processing unit being further configured to: compare the measured radon activity to the predetermined critical value (A crit); and output a radon determination signal for the sample collected within the probe if the radon activity is above the predetermined critical value (A ≥ A crit); the system further comprising: an optical sensor configured to detect volcanic ash in the air sample and output a volcanic ash detection signal, said processing unit being further configured to compare said volcanic ash detection signal output from the optical sensor to a predetermined critical value and output a volcanic ash determination signal, if the detection signal is equal to or above the critical value; said processing unit being further configured to issue a warning if both the radon determination signal and the volcanic ash determination signal are output for the same air sample. a detection system being configured for measuring radon activity and volcanic ash in the airspace in which the aircraft is flying, the detection system comprising: a probe configured for collecting air samples along a flight track of the aircraft in at least one chamber configured for measuring radon activity and volcanic ash in the air samples collected and configured for outputting a radon activity signal indicative of measured radon activity and a volcanic ash signal; and a processing unit configured to determine if the measured radon activity is above a predetermined critical value (A crit) representative for the flight altitude in which the air sample is collected within the probe, the processing unit being further configured to: compare the measured radon activity to the predetermined critical value (A crit); and output a radon determination signal for the sample collected within the probe if the radon activity is above the predetermined critical value (A ≥ A crit); the system further comprising: an optical sensor configured to detect volcanic ash in the air sample and output a volcanic ash detection signal, said processing unit being further configured to compare said volcanic ash detection signal output from the optical sensor to a predetermined critical value and output a volcanic ash determination signal, if the detection signal is equal to or above the critical value; said processing unit being further configured to issue a warning if both the radon determination signal and the volcanic ash determination signal are output for the same air sample. a probe configured for collecting air samples along a flight track of the aircraft in at least one chamber configured for measuring radon activity and volcanic ash in the air samples collected and configured for outputting a radon activity signal indicative of measured radon activity and a volcanic ash signal; and a processing unit configured to determine if the measured radon activity is above a predetermined critical value (A crit) representative for the flight altitude in which the air sample is collected within the probe, the processing unit being further configured to: compare the measured radon activity to the predetermined critical value (A crit); and output a radon determination signal for the sample collected within the probe if the radon activity is above the predetermined critical value (A ≥ A crit); compare the measured radon activity to the predetermined critical value (A crit); and output a radon determination signal for the sample collected within the probe if the radon activity is above the predetermined critical value (A ≥ A crit); the system further comprising: an optical sensor configured to detect volcanic ash in the air sample and output a volcanic ash detection signal, said processing unit being further configured to compare said volcanic ash detection signal output from the optical sensor to a predetermined critical value and output a volcanic ash determination signal, if the detection signal is equal to or above the critical value; said processing unit being further configured to issue a warning if both the radon determination signal and the volcanic ash determination signal are output for the same air sample. an optical sensor configured to detect volcanic ash in the air sample and output a volcanic ash detection signal, said processing unit being further configured to compare said volcanic ash detection signal output from the optical sensor to a predetermined critical value and output a volcanic ash determination signal, if the detection signal is equal to or above the critical value; said processing unit being further configured to issue a warning if both the radon determination signal and the volcanic ash determination signal are output for the same air sample.