How noisy is your airplane cabin?

DEVGRU      2018-11-13     2018-11-13 4 Comments

DEVGRU* (correspondence author), jimmy0017

Long-term exposure to ambient noise can lead to adverse effects on human health, and aircraft cabin is a typical noisy environment. Here, we report the cabin noise level of ten mainstream airframes (other than Boeing 747) based on 48 in situ measurements. Airbus A380 is the quietest plane in the sky. With the exception of Boeing 777, noise level and aircraft size is negatively correlated. Finally, there is no statistically significant difference between Boeing 787 and Airbus A350, while in general Airbus wide-body aircrafts are quieter than their Boeing counterparts.

Many studies have established the hazardous effects of the long-term exposure to high-intensity noise on the auditory and the nervous system. While federal and local laws have been enacted to regulate the noise level surrounding airports, no law currently applies to the noise level in an aircraft cabin. Studies have found that the cabin and the cockpit noise level do not exceed the noise limit established by the Occupational Safety and Health Administration, but the cabin noise level can directly impact the level of comfort experienced by the travelers. As a result, different cabin noise levels between different airframes, if they exist, should be taken into account when customers purchase air tickets.

In this regard, we obtained 48 sets of the cabin noise measurements on 46 flights since March 4th, 2017. Two pairs of such sets of measurements were measured on the same flight. Our survey covers the current mainstream airframes other than Boeing 747, including common long-haul aircrafts (Boeing 777, Airbus A380, and Airbus A330) and short- to medium-haul domestic aircrafts (Airbus A320, Boeing 737, and Boeing 757). The noise level on the latest-generation aircrafts (Boeing 787 and Airbus 350) were also measured. Here, we focused on the latitudinal difference of the cabin noise level between different aircrafts after they have entered the cruising altitude. While the absolute values of the noise level is of significance, we do not put emphasis on them because no absolute calibration was conducted. Detailed description of the analytical methods can be found in the Methods section.

The noise data is shown in Fig 1. To the first order, the noise level is negatively correlated with the size of the aircraft. The only exception is Boeing 777. Table 1 lists the detailed cabin noise data. Airbus A380 is the quietest aircraft with a cabin noise level of 56.0 ± 2.2 dB (2σ). For narrow-bodies, Airbus A320 and Boeing 737 have a noise level of 68.5 ± 3.4 and 69.6 ± 1.4 dB, respectively. We hypothesize that the noise level fundamentally depends on the distance to the aircraft engines. Therefore, although our measurements did not include Boeing 747, our hypothesis shall predict the noise level of 747 cabin to be quieter than 787 and to approach that of Airbus A380.

Fig 1. Cabin noise levels across different aircrafts

Only considering wide-body aircrafts, we found the Airbus airframes to be quieter than their Boeing counterparts. The major distinction comes from Boeing 777, the noise level of which is almost significantly higher than Airbus A350 and A330. This is most likely due to the use of GE90 engines on Boeing 777, which is the most powerful turbofan engine for commercial airliners.

Table 1. Cabin noise levels of different aircrafts at cruising altitudes

There is no statistically significant difference between Airbus A350 and Boeing 787, two latest airframes in the aviation industry, although our personal feeling suggests A350 being quieter. A lack of significant difference is mainly because of a small number of measurements. Future measurements specifically aiming the two aircrafts shall better constrain their respective cabin noise level.

Finally, while our data show that the noise level of all aircrafts we measured is no higher than 85 dB, a threshold for hazardous noise levels, we caution against comparing the absolute value of our noise measurements to various noise standards. That being said, our data shows the noise level reaching 70 dBon narrow-body airplanes and greater than 65 dB on Boeing 777, the backbone airframe on many intercontinental routes. It is therefore recommended that frequent flyers take protective precautions against the long-term exposure to the cabin noise, such as noise-cancelling headphones and ear plugs.

References

Omitted

Author Contributions

DEVGRU designed the research, collected and analyzed the data, and wrote the article. jimmy0017 collected the data.

Conflict of Interest

The author declares no conflict of interest.

Methods

Aircraft noise was measured on dB Meter Pro (iOS) on an Apple iPhone 7. The software records A-weighted acoustic pressure in decibel. The software was updated on Dec 7th, 2017, with no appreciable drift observed. The updated software had improved precision: the pooled standard deviation was 1.1 and 0.6 dB before and after the update, respectively. Therefore no correction was applied to pre- or post-update measurements.

Cabin noise was measured after the aircraft has reached the cruising altitude. This period of time was of significance due to its longest exposure time. While take-off and landing may be associated with higher levels of noise, they were not measured due to their relatively short durations.

Data measured prior to Oct 20, 2017 were based on a single measurement, the uncertainty of which was approximated by external reproducibility. The external reproducibility was measured in Oct 21, 2017 in a bathroom inside Sheraton Pasadena. The ambient noise level was measured 10 times and a standard deviation was calculated. The uncertainty of a single analysis then would be 2 times the standard deviation (2σ). The external reproducibility was 1.0 dB, close to the pooled standard deviation (1.1 dB) of all cabin measurements between Oct 20 and Dec 7, 2017 (when the software was updated). Out of 48 reported data points, 8 were based on one measurement.

After Oct 20, 2017, we took the average of 10 measurements of the cabin noise (a “block”) and used 2 times the calculated the standard error (2σ) to represent the uncertainties of each block. 40 data points contain such 10-measurement blocks, with a pooled standard deviation of 0.7 dB. As discussed above, the pooled standard deviation before and after the software update was 1.1 and 0.6 dB, respectively. In Fig 1, the uncertainty either represents (A) 2 times the external reproducibility if there is only one single measurement, or (B) 2 times the standard error of a 10-measurement block.

For a specific airframe, we calculate the average noise level of all blocks and used 2 times the standard error as the uncertainty reported in Table 1, representing a 95% confidence level, because the external reproducibility of different blocks of measurements across space and time is worse than the internal precision of each “block” (consisting of 10 measurements). This reported uncertainty integrates not only the analytical uncertainty of the software, but also the influences of varying flight path, cruising altitude, locations in the cabin, and aircraft engines.

Finally, in formulating Table 1 we did not take into account the difference among family models. For example, Airbus 320 consists of A319, A320, and A321. This is intended to increase the number of measurements for a specific aircraft model. Different engine manufacturers were not taken into consideration, either. For example two engine models can be found on Airbus A380: R&R Trent 900 and GP7000, but they were not differentiated, for the reason that customers would unlikely be informed of the engine information at the time of purchasing air tickets. We therefore incorporated this potential difference into the final expression of uncertainties.

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