2.2 How the Navy Misled the US FWS on the Noise Level of Growler Jets

How the Navy Misled the US FWS on the Noise Level of Growler Jets
(and why it this misinformation will cause permanent harm to spotted owls)

On August 12 2010, the US Fish and Wildlife Service issued a Biological Opinion regarding the impact of the US Navy's proposed expansion of the NW Training Range (NWTRC). (See USFWS Reference #13410-2009-F-0104). This Biological Opinion was required by Section 7 of the Endangered Species Act to determine any potential adverse impact of the Navy's proposed expansion on 11 endangered species including the Northern Spotted Owl and Marbled Murrelet. Based upon the information supplied by the Navy, which the US Fish and Wildlife Service assumed was accurate, the US Fish and Wildlife Service concluded that the Navy's proposed actions “may affect, but was not likely to adversely affect” the viability of the Marbled Murrelets population and were “not likely to adversely affect” (NLAA) the population of Northern Spotted Owls. We will show in this analysis that crucial information supplied to the US Fish and Wildlife Service was not accurate and that the Navy knew or should have known that this information was not accurate.

The request for Section 7 consultation was received by the US Fish and Wildlife Service on January 13 2009 regarding a proposed 5 year training plan for the US Pacific Fleet and the Northwest Training Range Complex. The limitation in the document to a 5 year period of time was ruled to be a violation of NEPA and the ESA by a federal court in September 2013. Here we will look more closely at a claim made in this Biological Opinion by the US Navy that the Navy Growler Jet emitted noise less than 90 decibels at a distance of 1,200 feet – when in fact, a growler jet pack emits noise at more than 120 decibels and possibly as high as 140 decibels at a distance of 1200 feet. Because sound doubles with every 10 decibels, 130 decibels is 16 times louder than 90 decibels.

The source of the Navy's claim was an Environmental Impact Statement an October 2008 Biological Evaluation (BE) that the Navy submitted to the US Fish and Wildlife Service on January 13 2009 as well as subsequent meetings and information exchanges between the Navy and the US Fish and Wildlife Service. Regarding the determination that the Northern Spotted Owls were “not likely to be adversely affected” (NLAA) by the Navy's proposed actions, the US FWS Biological Opinion stated on Page 2 of their Biological Opinion:

“These species were not addressed in the October 2008 Biological Evaluation provided by the Navy. The Navy concluded the effects of the NWTRC “may affect, are not likely to adversely affect” (NLAA) these listed species in the 27 October 2009 amendment to the original BE.”

This conclusion by the Navy in October 2009 was also based on grossly inaccurate information regarding the actual noise level of Growler jets at 1200 feet which the Navy claimed was less than 90 decibels when it was actually more than 120 decibels and possibly as high as 140 decibels.

On page 10 of the report, it states: “The Navy proposes a large increase in the annual number of events from the current 2,330 events (No-action Alternative) to a proposed 4,998 events under Alternative 2. In addition, the Navy proposes use of a new platform, the EA-18G, in up to 275 events annually.” Thus, the Navy wanted to double the number of training events and add a new and extremely noisy jet to the training – the EA-18G more commonly known as the Growler jet in addition to the prior EA-6B Prowler electronic warfare jets.

The location of the Growler jets was proposed to be in the airspace over the Olympic Military Operation Area (MOA) that had previously be designated as critical habitat for Northern Spotted Owls and Marbled Murrelets as part of the 1994 Northwest Forest Plan Record of Decision (ROD).

One of the “potential stressors” identified by the US FWS was “Acoustic” or above ambient sound levels due to the “operation of aircraft at law altitudes in the MOAs.” (page 16). These were called Aircraft Overflights on page 17 and Electronic Combat on page 18.

On page 19, the Biological Opinion refers to Endangered Species as “Resources” and states:
“Each stressor of interest is then described, to the extent possible, in terms of its‘ timing, duration, frequency, intensity, and location... Then, using the best available scientific and commercial data, we describe the likely response of all affected individuals (directly and indirectly) or designated critical habitat in the Response Analysis. Secondarily, we collate the effects on individuals and summarize them at the scale of the population(s) those individuals represent. This population-level summary of effects is then evaluated in terms of the likelihood of extinction posed by the Action, commonly referred to as the jeopardy analysis.”

On page 20, the Biological Opinion states: “The FWS uses the best scientific and commercial evidence available to support the analysis and finding within Biological Opinions.”

On page 57, the Biological Opinion states: “The fixed wing aircraft flying over the Olympic peninsula in the Olympic MOA will be at a minimum flight level of 6,000 ft msl or 1,200 ft AGL when above 6,000 ft msl; Rich Malaas, U.S. Navy, Naval Air Station, Whidbey Island, pers. comm. 2010). Northern spotted owl nest habitat occurs on the eastern side of the Olympic Peninsula up to 4,000 ft elevation, resulting in a minimum vertical separation (worst case) between nest habitat and Navy aircraft of 2,000 ft.”

Note: This is not what the current plan proposes. At public meetings, the Navy has indicated that vertical separation could be as little as 1200 feet. But for the purpose of this analysis ,we will assume that the plan is for 2,000 feet and seek confirmation of this from the Navy.

At the bottom of page 57 and top of page 58, the Biological Opinion states:
“The Navy reported sound transmission information for FA-18 and EA-6b jet aircraft commonly used in training missions (US Navy 2009a, p. 9, 10). At a horizontal distance of 4 nm (4.6 mi) from source, the received SPLs for these aircraft varied according to engine demand (descending, cruising, or climbing) with the reported values ranging from 39 dBA to 63 dBA for the FA-18 and 42 dBA to 62 dBA for the EA-6b. Although there is no potential for spotted owls to be exposed to the maximum peak sound level (Lmax) (U.S. Navy 2009a, p. 13) from an EA-6B climbing at 100 percent power, the distance to 92 dBA during an Lmax acoustic event would be a point approximately 3,500 ft (1,067 m) directly below the aircraft (U.S. Navy 2009a, p. 10). Based upon the SPL ranges reported by the Navy for jet aircraft used in the typical scope of training (above), we estimate a maximum received level of approximately 86 dBA (at 2000 feet) (See Footnote 2) in the forest canopy where spotted owls may be nesting.”

Footnote 2 states: “We derived this estimate from the general relationship of a 6 dB increase for every halving of the distance. With a received level of 63 dBA at 4.6 mi (24,288 ft) as the starting point (US Navy 2009a, p. 10), we expect the received levels from an aircraft at 2,000 ft above the forest canopy to be approximately 86 dBA.”

While there is a rule of 6 dB increase for every halving of the distance, this rule is only intended to be used over short changes in distance. Here the Navy deliberately misled the US Fish and Wildlife Service by supplying a sound measurement from 4.6 miles away rather than a sound measurement from 2000 feet away. Below is a graph showing visually the difference between 2000 feet and 24,288 feet.


Just because the sound is 63 decibels – or about a normal human conversation at 5 miles away does not mean the sound will only be 86 decibels at 2000 feet. Below is a table constructed using the 6 decibel rule and starting with the sound at 63 decibels at 24,288 feet.

The problem with the above table is that the Navy knows that the decibel reading of Growler jets is about 150 at 12 feet and 140 at 50 feet. Below is a graphic from a Navy study:


According to two Navy noise studies conducted in 2008 and 2009, the EA-18G Growler is louder than the F22 Raptor shown above. Here is a graphic from the Navy 2009 study comparing the loudness of various Navy jets. The EA-18G Growler is louder than the F-18 BD which is the loudest jet on the chart at 152 decibels compared to the F-22 at 146 decibels and the EA-6B at 148 decibels. My estimate based on several sources is that the EA-18G Growler is about 156 decibels – or almost twice as loud as the EA-6B.


Here is a link to an April 2009 Navy Jet Engine Noise study that the Navy should have supplied to the Fish and Wildlife Service and that the US Fish and Wildlife Service should have used to make their determination of noise levels because the 2009 Navy study is the latest and best available science on the subject of jet noise:

Below is a table adding a column using the 6 decibel rule starting at a reading of 150 decibels for 24 feet and subtracting 6 decibels for every doubling of the distance for the Growler and Prowler jets using the Navy 2008 and 2009 studies.


The Growler is so loud that there have been hundreds of complaints filed about it. The Navy knows about these complaints and knows that their flight crews have been going deaf due to the loudness of the Growler jets. So, the report the Navy gave to the US Fish and Wildlife Service understated the noise of the Growler jets by by 32 decibels. If we add 32 decibels to the maximum of 86 decibels calculated by the US FWS, we get a more accurate estimate of 118 decibels at 2000 feet or 124 decibels at 1000 feet. 118 decibels is four times louder than 86 decibels and 124 decibels is about 8 times louder than 86 decibels.

The above table indicates that the Navy reading of 63 decibels at 24,000 feet may have been in error. However, either way, it is not an acceptable scientific or statistical practice to estimate any number based upon a number that was different by a factor of ten. Put another way, no competent trained scientist would use a measurement taken from 4.6 miles away to estimate what the measurement might be from 2000 feet away. Instead, the US Fish and Wildlife Service should have asked for and the US Navy should have supplied the actual noise level from 2000 feet away.

This gross error was not the only gross error on the US FWS 2010 Biological Opinion. At the suggestion of the Navy, the US FWS also used a study of Mexican Spotted Owl (Delaney 1999) to conclude that Northern Spotted Owls would not be disturbed by noise levels of 90 decibels.

On page 58 of the 2010 US FWS Biological Opinion, it states:
“A slow rate of onset was offered as a partial (and important) explanation for the lower responses observed in Mexican spotted owls from helicopter overflights (Delaney et al. 1999). Second, the peak SPL of 86 dBA is generally considered below the threshold of 92 dBA (USFWS 2008) that could result in a significant disruption to essential behavior (i.e., breeding, feeding, or sheltering). We therefore conclude the response of spotted owls to aircraft overflights conducting training missions in the airspace over the Olympic Peninsula will not result in flushing or failed attempts by adults to feed nestlings. Therefore the effect to spotted owls from Naval aircraft training at 2,000 ft AGL over the Olympic Peninsula is considered to be insignificant.”

The USFWS 2008 conclusion of a 92 decibel disturbance threshold was also based on the 1999 Delaney study of Mexican Spotted Owls. Sadly, the Navy and US FWS Service failed to consider the fact that the single helicopter in the 1999 Delaney study was moving at less than 90 miles per hour (thus the slow approach) while the Navy Growler jets will be flying at speeds of up to 1,200 miles per hour (very fast approach) and will be flying in packs of three or more – which will double the intensity of the noise and lengthen the exposure of the noise.

(See Delaney, D. K., T. G. Grubb, P. Beier, L. L. Pater, and M. H. Reiser. 1999. Effects of helicopter noise on Mexican Spotted Owls. J. Wildl. Manage. 63:60-76).

Furthermore, the Navy and US Fish and Wildlife Service neglected to consider the fact that the Delaney study specifically recommended that owls not be exposed to more than one flyover per year while the Navy is proposing more than 35,000 flyovers per year for the next 10 to 20 years.

Combining 10 times faster aircraft speed and 16 times louder maximum noise level with 35,100 times more flyovers means that the Northern Spotted Owls would be subject to an impact that was 5.6 million times greater than the impact Mexican Spotted Owls were subjected to in the 1999 study used by the Navy to justify their proposed project.

Impact on Mexican Spotted Owls versus Impact on Northern Spotted Owls


Finally, the actual maximum noise level that northern spotted owls should be able to tolerate for significant periods of time is between 50 to 60 decibels. Below is a graphic of the US Navy claim that Northern Spotted Owls could tolerate 92 decibels and Growler jets only emitted 86 decibels versus a more accurate estimate that owls can only tolerate a maximum of 60 decibels while Growler jets fly at 130 decibels.


The actual noise level of a pack of growler jets at 1200 to 2000 feet of 130 decibels is 128 times louder than the actual owl disturbance threshold of 60 decibels. In fact, 130 decibels is almost certain to cause permanent hearing damage in Northern Spotted Owls.


Because the owls will suffer permanent hearing damage, they will not be able to use their extremely sensitive hearing for their night time foraging. As most of their foraging is at night – when they rely more on their hearing than on their sight, the owls will no longer be able to find adequate food. They will then starve to death which will cause a massive die off of owls – pushing their already fragile population over the edge of the extinction threshold.

Given that the US Navy permit to conduct flyovers is based upon false and misleading information supplied to the US Fish and Wildlife Service, and because this inaccurate information Navy military jet flyovers of spotted owl critical habitat are likely to cause severe permanent harm to northern spotted owls,it is essential that all Navy military flights over spotted owl critical habitat be halted immediately – and that the Navy be required to submit more accurate data to the US Fish and Wildlife Service as to the actual noise level of a pack of Growler jets during a 2000 foot flyover. It is also essential that the US Fish and Wildlife Service conduct a scientifically valid and reliable study to determine the actual noise disturbance threshold of Northern Spotted Owls.